GIFT  OF 
Dean  Frank  H.  Probert 


Mining  Dept 


THIS  BOOK 

is 
Dedicated 

to 

JAMES  M.  HYDE 
the  Pioneer 

of  the 

Froth-Flotation  Process 
in  America 


FLOTATION 


BY 


T.  A.  RICKARD 

EDITOR  OF  THE    MINING   AND   SCIENTIFIC   PRESS 
AND 

0.   C.   RALSTON 

U.    S.    BUREAU    OF    MINES 


PUBLISHED   BY  THE 

MINING  AND  SCIENTIFIC   PRESS 

SAN   FRANCISCO 


an T  Off 
DEAN  FRANK  H  -ROBERT 


OEPI. 


OEPI. 


COPYRIGHT,  1917 

BY 
DEWEY  PUBLISHING  Co. 


PREFACE 

This  is  a  report  on  recent  progress  in  the  application  of  flotation 
to  metallurgic  practice.  It  does  not  pretend  to  be  a  last  word.  No 
final  treatise  can  be  written  on  an  art  that  is  growing  as  flotation  has 
grown  during  the  last  two  or  three  years.  We  have  tried  to  give  the 
worker  the  latest  obtainable  information  on  the  technology  of  the 
subject,  believing  that  the  imperfection  of  our  presentation  will  be 
disregarded  in  his  eagerness  to  learn;  he  will  neither  misunderstand 
our  purpose  nor  belittle  our  intention.  To  those  that  expect  either  to 
hear  or  to  say  the  last  word  we  do  not  appeal ;  we  offer  this  book  in 

the  belief  that  it  will  be  useful ;  that  is  all. 

T.  A.  RICKARD. 
0.  C.  RALSTON. 


TABLE  OF  CONTENTS 

Page 

A  Glossary  of  Flotation T.  A.  Rickard  1 

The  History  of  Flotation T.  A.  RicTcard  9 

Principles  of  Flotation T,  A.  Rickard  34 

Testing  Ores  for  the  Flotation  Process.  .0.  C.  Ralston  and  Glenn  L.  Allen  75 

Differential  Flotation 0.  C.  Ralston  102 

Flotation  Oils  0.  C.  Ralston  121 

Ore  Flotation Wilder  D.  Bancroft  134 

The  Theory  of  Flotation '. H.  Hardy  Smith  146 

The  Flotation  of  Minerals Robert  J.  Anderson  154 

Principles  Underlying  Flotation , Joel  H.  Hildebrand  165 

Molecular  Forces  and  Flotation Will  H.  Coghill  172 

The  Armor  in  Flotation Will  H.  Goghill  193 

Electro-Statics  and  Flotation James  A.  Block  200 

Theory  of  Ore  Flotation H.  P.  Corliss  and  C.  L.  Perkins  211 

Flotation  at  the  Calaveras  Copper Hallett  R.  Robbins  228 

The  Horwood  Process  of  Flotation Allan  D.  Rain  239 

The  Disposal  of  Flotation  Products Robert  S.  Lewis  242 

Mechanical  Development  in  Flotation 0.  C.  Ralston  265 

Colloids  E.  E.  Free  305 

Flotation  Tribulations  Jackson  A.  Pearce  326 

Cost  Data 0.  C.  Ralston  335 

The  Control  of  Ore-Slime 0.  C.  Ralston  345 

The  Flotation  of  Oxidized  Ores Glenn  L.  Allen  and  0.  C.  Ralston  360 

The  Flotation  of  Gold  and  Silver T.  A.  Rickard  379 

Flotation  Litigation T.  A.  Rickard  397 


A  GLOSSARY  OF  FLOTATION 

ABSORB.  To  drink  in,  to  suck  up,  as  a  liquid  by  a  solid,  like  a  sponge  or 
fuller's  earth. 

ADSORB.  To  condense  and  hold  a  gas  on  the  surface  of  a  solid,  particularly 
metals.  Also  the  holding  of  a  mineral  particle  within  a  liquid  interface. 
From  L.  ad,  to,  and  sorbeo,  suck  in. 

ADHESION.  A  molecular  force  by  which  bodies  of  matter  are  caused  to 
stick  together. 

AGITATION  is  the  act  or  state  of  being  shaken,  stirred,  or  moved  with 
violence.  From  L.  agitatus,  agito,  the  frequentative  of  ago,  to  drive. 

BAFFLE.  That  which  defeats  or  frustrates,  hence  the  projections  or  wings 
that  divert  or  interrupt  the  flow  of  pulp  in  a  vessel. 

BUBBLE.  A  globule  of  air  or  other  gas  in  a  liquid;  also  a  vesicle  of  water 
or  other  liquid  inflated  with  air  or  other  gas. 

BUOY.     To  keep  from  sinking,  to  keep  afloat  in  a  liquid. 

COAGULATION.  The  state  of  a  solute  in  a  solvent,  or  of  a  colloidal  gel, 
resulting  from  clotting  or  curdling;  the  act  of  changing  to  a  curd-like  con- 
dition. 

COAL-TAR  is  a  thick,  black,  viscid,  and  opaque  liquid  condensed  when  gas 
is  distilled  from  coal.  This  product  consists  of  soluble  and  insoluble  sub- 
stances. 

COHESION.  That  force  by  which  molecules  of  the  same  kind  or  of  the 
same  body  are  held  together,  so  that  the  body  resists  being  pulled  to  pieces. 

COLLOID.  A  state  of  matter  supposed  to  represent  a  degree  of  sub-division 
into  almost  molecular  dimensions,  dispersed  in  a  solvent.  Colloidal  particles 
possess  the  property  of  carrying  electric  charges,  and  also  of  failing  to  dif- 
fuse through  a  membrane,  this  being  the  original  distinction  between  col- 
loids and  crystalloids. 

CONCENTRATE.  To  draw  or  gather  together  to  a  common  centre.  To  reduce 
to  a  purer  state  by  the  removal  of  non-essential  matter.  From  L.  con  or  cum, 
with,  and  centrum,  a  centre. 

CONTAMINATE.  To  make  impure  by  contact  or  admixture.  A  substance 
that  performs  the  function,  in  an  ore-pulp,  along  with  oil,  of  promoting  the 
emulsification  or  the  de-emulsification  of  the  oil,  and  thereby  exerts  an 
influence  upon  the  making  of  froth  for  the  flotation  of  minerals. 

DISPERSOID.    A  body  that  has  been  dispersed  in  a  liquid. 

EMULSION.  Milkification.  A  liquid  mixture  in  which  a  fatty  or  resinous 
substance  is  suspended  in  minute  particles  almost  equivalent  to  molecular 
dispersion.  From  L.  emulgeo,  to  drain  out,  in  turn  from  e,  out,  and  mulgeo, 
milk. 

FAT  is  a  white  or  yellowish  substance  forming  the  chief  part  of  adipose 
tissue.  It  may  be  solid  or  liquid;  it  is  insoluble  in  water;  when  treated  with 
an  alkali,  the  fatty  acid  unites  with  the  alkaline  base  to  make  soap. 

FILM.     A  coating  or  layer,  a  thin  membrane. 

FLOCCULENT  means  resembling  wool,  therefore  woolly.  Coalescing  and 
adhering  in  flocks.  A  cloud-like  mass  of  precipitate  in  a  solution.  From  L. 
floccus,  a  lock  of  wool. 

FLOTATION  is  the  act  or  state  of  floating,  from  the  French  flottaison,  water- 
line,  and  flotter,  to  float,  to  waft. 


FROTH.  A  collection  of  bubbles  resulting  from  fermentation,  effervescence, 
or  agitation. 

GANGUE.  The  non-metalliferous  or  non-valuable  metalliferous  minerals  in 
the  ore;  veinstone  or  lode-filling. 

GEL.  A  form  of  matter  in  a  colloidal  state  that  does  not  dissolve  but 
nevertheless  remains  suspended  in  a  solvent  from  which  it  fails  to  precipi- 
tate without  the  intervention  of  heat  or  of  an  electrolyte. 

GRANULATION  is  the  state  or  process  of  being  formed  into  grains  or  small 
particles.  From  L.  granum,  a  grain. 

GREASE.  Animal  fat  when  soft,  that  is,  in  a  semi-solid  state,  and  oily  or 
unctuous.  From  the  French  graisse. 

HYDROPHILIC.  A  property  possessed  by  colloids  whereby  they  take  up 
water  in  conjunction  with  the  molecules  of  the  colloid  in  a  manner  analogous 
to  a  closed  hydrated  molecule.  Hydrophilic  colloids  are  valuable  dispersing 
mediums  for  the  making  of  emulsions. 

LEVITATION.  The  act  of  rendering  light  or  buoyant.  L.  levitas,  lightness, 
from  levis,  light. 

METALLIC.  Of  or  belonging  to  metals,  containing  metals,  more  particularly 
the  valuable  metals  that  are  the  object  of  mining.  From  L.  metallum,  ore. 

MINERAL.  Inorganic  constituent  of  the  earth's  crust.  As  used  in  flotation 
the  terms  'mineral'  or  'metallic'  refer  to  those  valuable  constituents  in  the 
ore  that  it  is  the  object  of  the  process  to  separate  from  the  non-valuable  con- 
stituents, or  gangue. 

MOLECULE.  The  smallest  part  of  a  substance  that  can  exist  separately  and 
still  retain  its  composition  and  characteristic  properties;  the  smallest  com- 
bination of  atoms  that  will  form  a  given  chemical  compound.  From  F. 
molecule,  diminutive  from  L.  moles,  mass. 

OCCLUDE.  To  shut  or  close  in  pores  or  other  openings.  From  L.  ob, 
before,  claude,  close. 

OLEIC  ACID  is  the  fatty  acid  contained  in  olive-oil  combined  with  cresoline. 
Although  called  'acid,'  it  is  an  oily  substance  and  functions  as  oil  in  flotation 
operations;  it  is  contained  in  most  mixed  oils  and  fats,  from  which  it  is 
obtained  by  saponification  with  an  alkali.  From  L.  oleum,  oil. 

OIL  includes  (1)  fatty  oils  and  acids,  (2)  essential  oils,  mostly  of  vegetal 
origin,  such  as  eucalyptus  and  turpentine,  (3)  mineral  oils,  such  as  petro- 
leum products,  including  lubricating  oils. 

OSMOSE.  The  tendency  of  two  liquids  or  gases  to  mix  by  passing  through 
a  membrane  or  porous  wall  separating  them.  From  G.  osmos,  pushing. 

PULP  is  powdered  ore  mixed  with  water. 

SAPONIFICATION.  Conversion  into  soap;  the  process  in  which  fatty  sub- 
stances form  soap,  by  combination  with  an  alkali.  From  L.  sapo  (n-),  soap. 

SCUM.  Impure  or  extraneous  matter  that  rises  or  collects  at  the  surface 
of  liquids,  as  vegetation  on  stagnant  water,  or  dross  on  a  bath  of  molten 
metal. 

SKIN.    An  outside  layer,  coat,  or  covering.    From  A.  S.  scinn,  ice. 
SOLUTE.    The  substance  dissolved  in  a  solution. 

SURFACE-TENSION  is  the  contractile  force  at  the  surface  of  a  liquid  whereby 
resistance  is  offered  to  rupture. 

VISCOSITY  is  the  property  of  liquids  that  causes  them  to  resist  instan- 
taneous change  of  shape  or  of  the  arrangements  of  their  parts;  internal  fric- 
tion; gumminess.  From  L.  viscum,  birdlime. 


THE  HISTORY  OF  FLOTATION 

BY  T.  A.  RICKARD 

(From  the  Mining  and  Scientific  Press  of  March  17,  1917) 
INTRODUCTION 

The  various  flotation  processes  depend  upon  the  successful  applica- 
tion of  a  number  of  physical  principles,  of  which  three  may  be  in- 
stanced as  underlying  the  methods  successively  invented. 

1.  Film  suspension.  This  is  typified  by  the  floating  of  a  needle  on 
water.  In  the  familiar  experiment  a  small  needle  is  greased,  either  in- 
tentionally or  by  the  natural  oil  on  the  fingers;  but  when  pains  are 
taken  to  prevent  contact  with  anything  greasy,  the  needle  will  still 
float,  if  not  too  large  and  if  carefully  manipulated.1  If  the  needle  is 
too  large  it  will  not  float,  no  matter  how  skilfully  handled,  because  the 
force  of  gravity  overcomes  the  force  of  surface-tension,  which  is  the 
cause  of  this  kind  of  flotation.  Surface-tension  is  the  force  that  causes 
the  surface  of  a  liquid  to  resist. rupture.  This,  in  turn,  is  due  to  the 
fact  that  the  molecules  at  the  surface  have  a  greater  coherence  than 
the  molecules  within  the  body  of  the  liquid.  In  consequence,  the  sur- 
face acts  as  if  it  were  an  elastic  film. 

2.  Oil-buoyancy.  This  is  a  simple  manifestation  of  gravity, 
whereby  an  oil,  being  lighter  than  water,  will  rise  to  the  surface  of  a 
pulp  and  carry  with  it  any  mineral  particles  that  have  become  im- 
mersed in  it.  The  oil  plays  the  part  of  a  raft  or  boat.  In  order  to 
effect  flotation  the  volume  of  oil  must  be  such  that  its  smaller  specific 
gravity  will  overcome  the  greater  specific  gravity  of  the  burden  it  is 
to  bear  to  the  surface.  Most  oils  have  a  specific  gravity  of  about  0.9, 
as  against  the  1  of  water;  therefore  the  flotative  margin  is  10%  only. 
If  the  specific  gravity  of  a  mineral  is  5,  then  the  volume  of  oil  required 
to  buoy  it  must  weigh  more  than  40  times  as  much.  When  an  ore  con- 
tains 4%  of  a  mineral  having  a  specific  gravity  of  5,  then  more  than 
3200  pounds  of  oil  will  be  required  to  raise  the  mineral  in  a  ton  of 
ore  to  the  surface  of  the  pulp.  It  remains  to  add  that  oil  exhibits  a 
preference  for  certain  kinds  of  metallic  particles,  so  that  it  attaches 
itself  readily  to  them,  while  passing  the  particles  of  gangue.  The  lat- 


i'The  Flotation  Process.'     See  'Simple  Problems  in  Flotation,'  by  T.  A. 
Rickard.     Page  357. 


10.. 


FLOTATION 


ter,  therefore,  are  quickly  wetted  by  the  water,  and  sink.  The  oiling  of 
the  metallic  particles  enables  them  to  resist  wetting  and  lessens  their 
specific  gravity  so  that  in  the  presence  of  sufficient  oil  they  are  enabled 
to  float. 

3.  Bubble-levitation.  This  phase  of  flotation  depends  upon  the 
aid  of  bubbles  of  gas,  which,  by  attaching  themselves  to  particles  of 
mineral  buoy  them  to  the  surface,  like  cork-belts  or  the  bladders  that 
children  use  when  learning  to  swim.  Various  gases  have  been  tried, 
but  air  is  now  generally  used  for  the  making  of  bubbles.  The  attach- 
ment of  the  bubbles  to  the  metallic  minerals  in  preference  to  the 
gangue  has  been  said  to  be  due  to  an  affinity  or  selectiveness,  like  that 
of  the  oil,  and  the  presence  of  oil  is  said  to  enhance  it,  but  the  oiliness 
of  the  bubble-film  is  now  believed  to  be  the  chief  factor. 

In  order  that  the  bubbles  generated  in,  or  introduced  into,  a  pulp 
may  perform  their  metallurgic  function  they  must  last  long  enough  to 
carry  their  freight  not  only  to  the  surface  but  over  the  edge  of  the  con- 
taining vessel.  They  must  not  burst  untimely.  This  necessary  pro- 
longation of  bubble-life  is  effected  by  lowering  the  surface-tension  of 
the  water,  of  which  their  envelope  or  film  is  composed.  The  bursting  is 
due  to  the  contractile  force  of  surface-tension,  and  it  must  be  moder- 
ated if  the  bubble  is  to  last  long  enough.  A  decrease  of  surface-ten- 
sion is  produced  by  putting  some  impurity  or  contaminant  in  the  water. 
Heretofore  oil  has  been  the  contaminant  chosen,  as  soap  is  used  by  a 
school-boy  to  blow  his  bubbles,  he  having  discovered  that  the  bubbles 
blown  in  pure  water  are  too  fragile  for  his  play.  The  use  of  oil  was  in- 
herited from  the  prior  art,  but  other  re-agents  are  likely  to  be  found 
adequate  for  the  purpose. 

Thus  the  third  and  most  successful  phase  of  flotation  has  grown  out 
of  the  second,  although  it  is  more  nearly  the  logical  development  of  the 
first  phase.  Film-suspension  involves  the  aid  of  air,  for  the  floating  of 
pulverized  minerals  on  the  surface  of  water  is  helped  by  the  air  en- 
trained in  the  ore.  The  attempt  to  invent  an  effective  method  out  of 
oil-buoyancy  instead  of  film-suspension  goes  far  to  explain  the  delay 
that  marked  the  development  of  this  metallurgic  process. 

EARLY  ATTEMPTS 

The  story  of  the  slow  and  toilsome  development  of  this  metallur- 
gical process  may  claim  to  be  'historical'  if  only  for  the  fact  that  the 
use  of  oil  for  collecting  metals  was  mentioned  by  Herodotus.  The  re- 
covery of  gold  from  the  mud  of  a  lake  by  means  of  feathers  daubed 
with  pitch  and  held  in  the  hands  of  apocryphal  virgins  is  as  pertinent 


THE    HISTORY    OF    FLOTATION  11 

to  the  subject  as  the  yarn,  2000  years  later,  of  a  young  school-teacher 
in  Colorado  who  was  washing  oil-stained  ore-sacks  in  her  brother's  as- 
say-office when  she  noted  that  the  pyrite  floated  on  the  water  contam- 
inated by  the  oil.  We  know  now  that  the  Carrie  Everson  fabricated 
in  the  course  of  litigation  is  a  myth  and  that  while  there  was  a  lady  of 
that  name,  she  was  the  wife  of  a  Chicago  doctor.  Indeed,  there  is  rea- 
son to  believe  that  Dr.  William  K.  Everson,  of  Chicago,  not  his  wife, 
was  the  originator  of  the  method  that  was  patented.  The  death  of  the 
husband — the  real  inventor — prevented  the  development  of  the  process, 
which  fell  into  the  hands  of  less  competent  persons,  Thomas  Criley  and 
Charles  Hebron,  in  collaboration  with  whom  Mrs.  Everson  devised  a 
method  based  on  "the  chemical  affinity  of  oils  and  fatty  substances 
for  mineral  particles"2  and  obtained  a  patent  in  1885.  She  and  her 
husband  did  ascertain  that  " acidification  of  the  ore-pulp  is  necessary 
for  the  sharp  oil-differentiation  of  mineral  from  gangue."3  But  the 
method  patented  by  her  in  1885  was  a  complete  failure  as  a  metallur- 
gical process,  although  it  probably  did  serve  to  suggest  some  of  the 
later  investigations  and  it  was  used  freely  in  the  attempt  to  disprove 
the  originality  of  subsequent  inventions.  The  odds  were  greatly 
against  Mrs.  Everson :  she  was  a  woman,  her  idea  seemed  absurd,  she 
had  no  mechanical  ingenuity  herself  nor  was  any  at  her  command,  and 
she  had  no  financial  backing.  If  we  consider  these  circumstances,  we 
shall  not  wonder  at  her  failure  to  develop  a  concentration  process. 

The  first  patent  employing  oil  for  a  metallurgical  purpose  was  that 
obtained  by  William  Haynes  in  England  in  1860.  This  is  of  academic 
interest  as  being  a  prelude  to  flotation.  By  mixing  coal-tar  and  resin 
with  crushed  ore,  in  the  proportion  of  5:  9,  he  made  a  "dough"  that 
held  the  metallic  particles,  while  the  gangue  was  removed  by  the  help 
of  water  and  "frictional  trituration. "  The  idea  proved  wholly  im- 
practicable and  is  only  worthy  of  mention  as  the  first  recorded  use  of 
oil — an  oil  partly  soluble — in  the  concentration  of  ores.  The  next  at- 
tempt is  that  of  Hezekiah  Bradford,  an  American,  who,  in  1885,  two 
months  before  the  date  of  Mrs.  Everson 's  patent,  obtained  a  patent 
for  the  first  method  that  was  based  upon  a  recognition  of  the  surface- 
tension  of  water  in  contact  with  air.  His  method  was  one  for  * '  saving 
floating  materials  in  ore-separation,"  such  as  escaped  from  arrest  by 
tables,  vanners,  and  jigs.  He  stated  : 

"These  floating  particles  appear  to  possess  some  peculiar  quality 


2As  stated  by  her  son.    'Carrie  J.  Everson  and  Flotation,'  M.  &  S.  P.,  Janu- 
ary 15,  1916. 

3H.  L.  Sulman,  Presidential  address.    Trans.  I.  M.  &  M.,  Vol.  XX,  page  14. 


12  FLOTATION 

which  repels  water  from  their  surface,  especially  when  such  particles 
are  exposed  even  momentarily  to  atmospheric  air,  and  when  such  ex- 
posure takes  place  the  water  is  repelled  from  a  sufficient  portion  of 
their  surfaces  to  cause  such  particles  to  float  off  on  the  surface  of  the 
waste  water  from  the  other  particles  that  sink  in  the  water. ' ' 

He  had  the  germ  of  an  idea  pregnant  with  metallurgic  possibility, 
but  it  was  still-born.  Haynes  and  Bradford  had  inklings  of  the  phys- 
ical phenomena  underlying  the  flotation  process,  but  they  were  pio- 
neers that  blazed  no  trail  and  crossed  no  range  of  fruitful  discovery. 
Carrie  J.  Everson  comes  next  in  point  of  time.  Her  groping  after 
a  practical  process  is  noteworthy  by  reason  of  the  introduction  of  acid, 
but  her  trail  also  stopped  at  the  foot  of  the  talus  on  the  slope  of  the 
range.  The  patent  records  disclose  other  abortive  attempts  in  the 
same  direction  during  the  ensuing  decade,  but  none  is  of  any  con- 
sequence except  H.  L.  Sulman's  British  patent  of  1893,  in  which  he 
describes  a  means  for  saving  'float'  gold  by  adding  something  to  the 
mill-water  that  will  diminish  its  surface-tension.  This  is  interesting 
as  recording  scientific  curiosity  concerning  the  physics  of  flotation  on 
the  part  of  a  metallurgist  that  was  destined  to  contribute  so  greatly  to 
the  decisive  development  of  the  process.  His  successful  participation 
is  due,  in  part,  to  his  having  been  formerly  engaged  professionally  in 
the  chemistry  of  the  oil  and  soap  industries,  for  thereby  he  acquired 
knowledge  of  a  kind  that  proved  of  great  value  to  him  at  a  later  date. 

So  far  no  workable  method  had  been  invented — only  ingenious 
schemes  and  impracticable  proposals. 

The  next  incident  in  this  story  brings  us  to  the  edge  of  real  achieve- 
ment. In  1894  George  Robson,  for  himself  and  Samuel  Crowder,  pat- 
ented a  process  for  separating  sulphides  from  gangue.  He  disclaimed 
"the  use  of  acid  or  salts  and  also  the  method  of  washing  away  the  gan- 
gue with  water,"  and  appears  therefrom  to  have  been  aware  of  the 
earlier  patents.  He  effected  "the  separation  of  the  metallic  matter  by 
the  mixture  of  oils  alone. ' '  Thus  he  followed  in  the  track  of  Haynes. 
The  proportion  of  oil  was  large :  as  much  as  three  times  the  weight  of 
ore.  It  was  a  method  of  buoying  the  sulphide  particles  with  oil.  The 
process  was  tried  on  a  working  scale  at  the  Glasdir  gold  mine  in  Wales 
and  was  commended  by  James  Brothers,  a  firm  of  experienced  metal- 
lurgists. But  it  did  not  succeed  and  apparently  led  nowhere.  Yet  it 
opened  the  way  for  a  decisive  event  namely,  the  technical  participation 
of  the  Elmore  brothers. 

ELMORE 

Francis  Edward  Elmore  was  a  trained  engineer  with  an  inventive 


THE    HISTORY    OF    FLOTATION  13 

mind.  His  father,  William  Elmore,  bought  the  Glasdir  mine  from 
Samuel  Crowder,  in  1896.  The  conventional  concentrating  plant,  of 
jigs  and  shaking  tables,  had  proved  unable  to  make  a  good  recovery  of 
the  gold-bearing  chalcopyrite  in  the  ore  from  this  Welsh  mine.  The 
elder  Elmore  sent  his  two  sons,  Francis  Edward  and  Alexander  Stan- 
ley, to  investigate.  It  has  been  stated4  by  Stanley  Elmore  that,  on  the 
occasion  of  one  of  their  visits  to  the  mill,  his  brother  Frank  noticed 
copper  adhering  to  the  oil  that  had  dropped  from  a  shaft-bearing,  and 
thus  obtained  the  idea  of  his  invention :  ' '  Finely-divided  wet  copper- 
pyrite  would  adhere  to  a  greasy  surface,  whereas  finely-divided  wet 
rock  would  not. ' '  But  no  accidental  demonstration  of  the  action  of  oil 
was  necessary  to  arouse  Mr.  Elmore  '&  interest  in  face  of  the  fact  that 
Eobson  had  conducted  experiments  in  oil -flotation  on  the  same  spot. 
We  have  the  testimony  of  Mr.  Crowder  himself,5  now  a  very  old  man, 
that  Robson's  experimental  oil-concentration  plant  was  on  the  mine 
when  it  was  purchased  by  William  Elmore,  and  we  know  also,  from 
Mr.  Crowder,  that  he  wrote  to  Stanley  Elmore  in  1897  urging  him  to 
use  oil  as  a  means  of  concentration.  In  1898  Frank  Elmore  obtained 
his  first  patent.  A  working  unit  of  full  size  was  erected  at  the  Glasdir 
mine.  Walter  McDermott,  Hennen  Jennings,  and  Wernher,  Beit  & 
Co.,  gave  the  Elmores  their  financial  support  and  formed  a  syndicate, 
which  became  known  as  the  Ore  Concentration  Syndicate.6 

In  his  patent  Frank  Elmore  describes  the  process  as  "mixing  the 
pulverized  ore  first  with  water  in  considerable  quantity,  then  adding 
to  the  mixture  an  oil  of  the  kind  described,  which' adheres  to  the  metal- 
lic constituents  but  not  to  the  wet  rocky  constituents."  He  used  a 
thick  oil  and  introduced  the  idea  of  the  freely  flowing  pulp  as  against 
the  mixing  of  oil  with  crushed  ore  in  the  presence  of  only  a  small  pro- 
portion of  water,  as  Robson  and  Crowder  had  done.  By  using  more 
water,  he  also  entrained  more  air,  so  essential  to  success,  although  he 
did  not  then  recognize  this  fact? 

In  the  first  plant,  at  the  Glasdir  mine,  the  mixture  of  crushed  ore 
and  water  was  fed  at  the  upper  end  of  a  slowly  revolving  drum,  pro- 
vided with  annular  helical  ribs  and  tranverse  blades,  so  as  to  mix  the 
pulp  and  oil  without -producing  emulsification.  The  oil  was  intro- 
duced through  a  separate  pipe.  The  mixture  was  discharged  into  a  V- 
shaped  vessel,  where  the  water  and  sand  subsided,  while  the  oil  buoyed 
the  sulphide  particles  to  the  top.  An  oil-residuum  of  0.89  specific 


4M.  &  S.  P.,  September  23,  1916. 
BM.  &  S.  P.,  February  24,  1917,  and  June  16,  1917. 

sin  1905  it  acquired  the  Elmore  vacuum  patents  and  became  the  Ore  Con- 
centration Company. 


14  FLOTATION 

gravity  was  used  in  equal  parts  by  weight  with  the  ore,  ton  for  ton. 
The  oil  was  so  viscous  as  to  require  the  aid  of  small  rotary  pumps  to 
move  it  forward.  The  temperature  of  the  oil  and  water  was  kept  be- 
tween 54°  and  57°  F.  The  loss  of  oil  was  2  gallons  per  ton  of  ore.  A 
concentration  of  14:1  was  achieved  with  a  recovery  (in  the  concen- 
trate) of  69%  of  the  gold,  65%  of  the  silver,  and  70%  of  the  copper 
from  chalcopyritic  ore  assaying  1.12%  . copper,  0.49  oz.  gold,  and 
0.8  oz.  silver  per  long  ton.  These  details  are  taken  from  a  paper 
by  C.  M.  Rolker  read  before  the  Institution  of  Mining  and  Metallurgy, 
on  April  25,  1900.  Mr.  Rolker  described  the  process  as  "somewhat 
dirty  and  nasty,"  but  he  stated  that  "the  mechanical  contrivances 
brought  into  action  by  the  inventor  are  excellently  adapted  to  the  work 
demanded,  and  bespeak  very  careful  thought,  as  well  as  patient,  sys- 
tematic, and  highly  intelligent  work. ' ' 

The  discussion  of  Mr.  Rolker 's  paper,  as  recorded  in  the  Transac- 
tions of  the  Institution,  show's  clearly  that  nobody  at  that  time  recog- 
nized the  part  played  by  air  in  the  process  of  notation.  Stanley  El- 
more  has  cited  the  use  of  a  Gabbett  mixer,  which  causes  a  violent  agi- 
tation with  indrawing  of  large  "quantities"  of  air7  as  proof  that  he 
and  his  brother  were  ' '  quite  cognizant  of  the  fact  that  it  was  the  air  en- 
trapped in  the  bulk  of  the  oil  which  rendered  it  capable  of  carrying 
more  than  its  theoretical  load  of  concentrate."  But  this  use  of  the 
Gabbett  machine  was  made  in  1902,  by  which  time  the  action  of  air  had 
begun  to  be  understood.  During  the  discussion  of  the  Rolker  paper, 
two  years  earlier,  nobody  present  had  been  able  to  explain  why  the  ac- 
tual load  of  concentrate  had  been  150%  more  than  was  accountable  to 
the  difference  in  specific  gravity  between  the  oil  and  the  water.  The 
manager,  John  Bevan,  had  testified  that  the  flotative  efficiency  of  the 
oil  was  25%,  against  the  theoretical  load  of  10%,  on  an  oil  of  0.9  spe- 
cific gravity;  whereupon  Frank  Elmore  remarked:  "It  seems  rather 
strange  that  there  should  be  such  a  difference  between  theory  and  prac- 
tice." On  the  same  occasion  Mr.  Rolker  said:  "The  viscosity  of  the 
oil  is  the  all-important  point."  Neither  H.  L.  Sulman  nor  H.  F.  K. 
Picard,  both  of  whom  took  part  in  the  discussion,  made  the  slightest 
reference  to  the  agency  of  air,  which  was  entrained  with  the  ore  and 
water  while  they  were  being  mixed  in  the  revolving  drum.  As  late  as 
January  1903  Stanley  Elmore  took  out  a  patent  for  an  improved  ap- 
paratus wherein  air  was  excluded  from  the  operation  of  concentration 
by  oil.  But  his  is  not  the  only  attempt  to  read  the  past  in  terms  of  the 
present — all  the  litigants  have  done  it  and  many  of  their  witnesses. 


7M.  &  S.  P.,  September  23,  1916,  page  452. 


THE   HISTORY   OF   FLOTATION  15 

The  fact  is  clear  that  in  1900  the  agency  of  air  was  not  understood  by 
any  of  the  exponents  of  flotation. 

In  1901  the  Elmore  syndicate  established  a  demonstration  plant  in 
London  and  the  free  access  thereto  given  to  the  mining  profession,  to- 
gether with  the  frequent  publication  of  information  concerning  the 
process,  did  a  great  deal  to  stimulate  interest  and  curiosity,  contribut- 
ing thus  to  the  later  improvements  whereby  the  process  was  turned  in- 
side-out and  made  supremely  valuable  to  the  mining  industry.  A  num- 
ber of  plants  were  built  to  apply  the  bulk-oil  process,  at  mines  scat- 
tered all  over  the  world,  notably  the  Namaqua.  in  South  Africa,  the 
Le  Roi  No.  2  in  British  Columbia,  the  Tywarnhaile  in  Cornwall,  and 
the  Sygun  in  Wales,  but  it  cannot  be  said  that  any  one  of  them  was  an 
unquestioned  metallurgical  success. 

At  this  time  the  treatment  of  low-grade  complex  zinc-lead  ore  at 
Broken  Hill,  and  more  particularly  the  beneficiation  of  dumps  of  sim- 
ilar material  discarded  in  the  course  of  large-scale  milling  operations, 
began  to  stimulate  efforts  to  add  some  form  of  flotation  to  the  conven- 
tional concentration  process.  Hence  the  next  chapter  of  the  story 
concerns  itself  mainly  with  the  work  of  a  group  of  Australian  metal- 
lurgists. 

FLOTATION  AT  BROKEN  HILL 

After  various  attempts  at  magnetic  separation  had  failed,  an  effort 
was  made  to  employ  flotation  for  the  purpose  of  treating  the  huge  ac- 
cumulations of  tailing,  which  averaged  16  to  20%  zinc,  5  to  10%  lead, 
and  5  to  15  oz.  silver  per  ton. 

In  January  1902,  Charles  V.  Potter,  an  Australian  engineer,  ob- 
tained a  British  patent  for  the  flotation  of  sulphides  in  a  hot  acid  so- 
lution. He  used  a  stirrer  and  claimed  that  the  solution  would  ' '  react 
on  the  soluble  sulphides  present  to  form  bubbles  of  sulphuretted  hy- 
drogen on  the  ore  particles  and  thereby  raise  them  to  the  surface." 
Here  we  have  the  first  suggestion  of  the  bubble  idea.  In  November  of 
the  same  year  Guillaume  D.  Delprat,  manager  of  the  Broken  Hill  Pro- 
prietary mine,  applied  for  a  similar  patent,  except  that  he  used  salt- 
cake  instead  of  sulphuric  acid.  In  his  first  American  patent,  No.  735,- 
071,  filed  on  January  2,  1903,  Mr.  Delprat  states  that  his  process  "  de- 
pends upon  the  ore  particles  being  attacked  by  the  acid  to  form  a  gas. 
Each  ore  particle  so  attacked  will  have  a  bubble  or  bubbles  of  gas 
adhering  to  it,  by  means  of  which  it  will  be  floated  and  can  be 
skimmed  or  floated  off  the  solution."  In  another  place  he  says  spe- 
cifically :  ' '  The  sulphides  in  the  ore  are  rapidly  attacked  by  the  acid 
and  gas-bubbles  formed  on  them,  that  quickly  carry  them  to  the  sur- 


16  FLOTATION 

face."  In  this  and  in  Potter's  patent  we  have  the  earliest  recognition 
of  bubble-levitation.  It  is  true,  we  have  been  told8  of  ' bubbles'  being 
mentioned  in  connection  with  an  experiment  made  in  1889  at  Baker 
City,  Oregon,  where  the  Everson  method  was  the  subject  of  experiment, 
but  the  word  was  applied  to  the  champagne  that  was  the  penalty  of  a 
bet,  rather  than  the  process  itself.  A  story  told  in  1915  is  apt  to  read 
into  the  happenings  of  1889  much  that  was  unknown  at  the  earlier 
date.  Oil  and  acid  were  the  agents  in  those  futile  efforts  at  flotation 
made  by  Thomas  F.  Criley  at  Baker  City,  but  it  is  worthy  of  mention 
that  the  fine  grinding  of  wet  ore  in  the  presence  of  sulphuric  acid  must 
have  been  accompanied  by  the  generation  of  hydrogen  and  probably  of 
carbon  di-oxide  also,  if  the  pulp  contained  either  calcite  or  metallic 
carbonates. 

Potter  and  Delprat  were  mistaken  in  the  reactions  that  were  sup- 
posed to  follow  the  introduction  of  the  acid,  whether  it  was  the  sul- 
phuric, the  nitric,  or  the  sodium  bi-sulphate  that  they  used  variously. 
At  that  time  it  was  believed  that  the  sulphuric  acid  reacted  with  the 
sulphides  to  form  hydrogen  sulphide  without  attacking  the  gangue.9 
Then  it  was  suggested  that  carbon  di-oxide  was  generated  by  decompo- 
sition of  a  carbonate  encrustation  on  the  sulphides,  due  to  weathering 
of  the  ore,  arguing  therefrom  that  it  was  necessary  for  the  gas  to  be 
produced  at  the  surface  of  the  sulphide  particles.  Such  explanations 
overlooked  the  simple  fact  that  the  Broken  Hill  ore  contains  a  consid- 
erable proportion  of  carbonates,  notably  calcite,  siderite,  and  rhodo- 
crosite.  From  any  of  these  a  warm  acid  solution  would  release  the  car- 
bon di-oxide  gas  that  promptly  attached  itself  to  the  surface  of  the 
metallic  particles. 

The  processes  of  Potter  and  Delprat  have  been  labeled  under  '  acid- 
flotation'  and  'surface-tension'  methods.  In  their  original  form,  it  is 
true,  they  did  not  include  the  use  of  oil,  and  the  apparatus  pictured 
in  Delp rat's  patent  (U.  S.  No.  768,035)  suggests  the  surface-tension 
method  of  Bradford,  but  the  use  of  a  baffle  ' '  to  insure  the  total  immer- 
sion of  all  particles  of  ore  in  the  fluid  or  liquor"  indicates  that  surface- 
tension  in  its  simplest  form,  as  used  later  by  H.  E.  Wood,  for  example, 
was  not  a  principal  agent.  In  Potter's  apparatus — a  pointed  box — 
the  feed  has  to  pass  under  the  surface  and  is  wholly  submerged,  so  that 
surface-tension  again  is  not  given  free  play,  although,  of  course,  it  is  a 
factor  in  the  formation  of  the  bubbles  that  buoy  the  sulphides  to  the 


«Ben.  S.  Revett,  M.  &  S.  P.,  October  16,  1915,  page  590. 

o'The  Physics  of  Ore  Flotation,'  J.  Swinburne  and  G.  Rudorf,  M.  &  S.  P., 
February  24,  1906. 


THE    HISTORY   OF    FLOTATION  17 

surface  after  the  pulverized  ore  has  been  mixed  thoroughly  with  the 
acidulated  water. 

In  August  1904,  Auguste  J.  F.  De  Bavay  patented  a  process  re- 
sembling that  of  Bradford.  He  used  neither  acid  nor  oil,  depending 
entirely  upon  the  effect  of  surface-tension  to  form  a  film  of  sulphide 
particles  while  allowing  the  particles  of  gangue  to  sink.  The  company 
formed  to  exploit  his  patents  claimed  that  the  process  worked  without 
either  oil  or  acid,  but  it  was  admitted  that  the  notation  was  improved 
thereby,  and  both  oil  and  acid  were  used  at  a  later  date.  In  1910  his 
rights  were  transferred  to  Amalgamated  Zinc,  Ltd.,  and  in  1912  this 
company  was  annexed  by  Minerals  Separation,  Ltd.  De  Bavay 's 
method  was  employed  on  a  large  scale  at  the  North  Broken  Hill  mine 
and  in  a  plant  for  treating  the  dumps  of  the  South  and  Block  10  mines. 
It  is  also  used  on  current  zinc-tailing  produced  at  the  North  and  South 
mines.  Treatment  is  confined  mainly  to  material  free  from  slime.  In- 
deed, none  of  the  earlier  processes,  the  Potter,  Delprat,  De  Bavay, 
Cattermole,  or  Elmore  did  good  work  on  slime — at  Broken  Hill. 

The  operation  of  some  of  these  Australian  methods  of  flotation  with- 
out oil  is  an  interesting  feature.  Most  of  them  treated  old  dumps  and 
it  is  well  to  note  T.  J.  Hoover's  suggestion10  that  "there  may  be  or- 
ganic substances  in  the  ore  which,  upon  the  addition  of  acid,  yield 
gummy  organic  compounds  that  selectively  adhere  to  the  ore."  The 
research  of  recent  years  has  disclosed  the  fact  that  a  large  variety  of 
soluble  frothing  agents  are  effective  and  that  a  number  of  shrubs  yield 
derivatives  capable  of  replacing  oil  in  the  flotation-cell. 

In  1903  a  Potter  plant  was  erected  to  treat  middling  from  the  lead- 
concentrator  on  Block  14.11  Concurrently  the  Delprat  process  was 
adopted  by  the  Broken  Hill  Proprietary,  the  plant  being  increased  suc- 
cessively from  its  original  capacity  of  3500  to  6250  tons  per  week.  Lit- 
igation ensued  between  these  two  Australian  patentees.  This  ended  in 
a  compromise  whereby  Potter  was  eliminated ;  but  it  is  worthy  of  note 
that  Potter's  method  was  the  first  flotation  process  to  be  used  success- 
fully on  a  working  scale. 

In  1905  the  Zinc  Corporation  was  formed  to  purchase  and  treat 
several  large  dumps.  In  1906  the  Potter  process  was  used  by  this  com- 
pany on  the  British  Broken  Hill  Proprietary  dump,  from  which  a 
concentrate  was  obtained  containing  44%  zinc,  8%  lead,  and  8  oz.  sil- 


lo'Concentrating  Ores  by  Flotation.'    Page  101. 

nThe  superintendent  of  this  mill  was  Henry  Lavers,  whose  name  is 
notable  in  the  history  of  the  process. 

isThese  figures  refer  to  the  final  test  made  by  W.  E.  Simpson  on  a  mixture 
of  tailings  from  all  the  dumps  owned  by  the  Zinc  Corporation. 


18  FLOTATION 

ver,  representing  a  recovery  of  81%  zinc,  55%  lead,  55%12  silver,  at 
a  cost,  including  transport,  of  50  cents  per  ton.  H.  C.  Hoover  testified 
in  court  that  the  Potter  process,  as  used  by  the  Zinc  Corporation, 
"proved  a  commercial  failure;  for  the  later  results,  after  the  mill  was 
remodeled,  were  not  as  good  as  those  just  quoted."  In  1907  the  Min- 
erals Separation  process  was  adopted  in  a  plant  erected  under  the  di- 
rection of  the  patentees,  but,  as  Mr.  Hoover  says,  it  "also  proved  a 
failure,13  and  after  exhaustive  trials  the  Elmore  notation  process  was 
introduced  and  found  successful. ' '  He  refers,  of  course,  to  the  Elmore 
vacuum  process,  which  was  used  by  the  Zinc  Corporation  chiefly  on 
jig-middling  from  the  Block  10  mill,  until  1910,  when,  on  the  advice 
of  his  brother,  T.  J.  Hoover,  the  improved  Minerals  Separation  process 
was  substituted,  because  it  promised  to  give  better  results  on  slime 
and  because  most  of  the  coarse  material  of  the  tailing-dumps  had  been 
milled  by  that  time. 

As  early  as  1902,  while  working  with  the  granulation,  or  Catter- 
mole,  process  in  the  Central  mill,  the  scum  of  slime  made  from  re- 
crushed  tailing  was  saved  by  floating  it  over  a  spitz-box.  W.  Shell- 
shear  and  F.  A.  Beauchamp  suggested  the  application  of  this  idea  to 
correct  the  failure  of  the  granulating  process  caused  by  floccules  of 
mineral  breaking  away  from  the  granules  on  the  tables.  The  sugges- 
tion was  put  aside  until  1903,  when  a  small  spitz-box  was  tried.  It 
was  ascertained  that  the  flotation  effect  was  produced  while  using  9  Ib. 
oil  and  22  Ib.  acid  per  ton  of  ore.  The  proportion  of  oil  was  decreased 
gradually  to  2  Ib.  per  ton.  This  was  the  real  beginning  of  froth-flota- 
tion.14 

The  first  mill  to  use  the  Sulman  &  Picard  modification  of  the  agita- 
tion-froth process,  as  recorded  in  U.  S.  patent  835,120,  was  the  one  at 
the  Central  mine,  built  in  1905,  as  previously  mentioned.  In  1907  a 
new  mill  was  finished  and  by  1908  the  recovery  had  been  improved  to 
85.5%  of  the  zinc,  82.5%  of  the  lead,  and  83.8%  of  the  silver,  on  a  ma- 
terial assaying  21.4%  zinc,  6%  lead,  and  8.6  oz.  silver  per  ton,  yield- 
ing a  concentrate  assaying  42.5%  zinc,  11.4%  lead,  arid  16.6  oz.  silver 
per  ton.  Concentration  was  in  the  ratio  of  7 :  3. 
;*iGr>  '.' 

FROMENT 

The  scene  shifts  from  Australia  to  Italy.    At  the  time  when  Pot- 


because  the  plant  was  over-loaded  to  about  double  its  capacity. 
i*It  has  been  asserted  that  this  method  was  discovered  by  the  mill-men  in 
the  Central  plant  at  Broken  Hill  and  that  the  M.  S.  representative  then  cabled 
to  the  London  office  about  it.     The  account  given  by  Mr.  Hebbard  is  not  con- 
tradictory. 


THE    HISTORY    OF    FLOTATION  19 

ter  and  Delprat  introduced  their  methods  at  Broken  Hill,  another  in- 
vestigator was  about  to  contribute  his  quota  to  the  development  of  flo- 
tation. The  Elmore  bulk-oil  method  had  been  seen  by  Alcide  Froment 
at  the  Traversella  mine,  in  Italy,  where  he  was  engaged  as  an  engineer 
in  1901,  when  he  invented  what  he  himself  termed  * '  a  modification  of 
what  is  known  as  the  oil  process  of  concentration. ' '  His  modification — 
patented  in  June  1902 — was  to  introduce  a  gas  into  the  freely  flowing 
oiled  pulp  used  by  Elmore.  He  argued,  in  his  patent,  that  "if  a  gas 
of  any  kind  is  liberated  in  the  mass  the  bubbles  of  the  gas  become 
coated  with  an  envelope  of  sulphide  and  thus  rise  readily  to  the  surface 
of  the  liquid  where  they  form  a  kind  of  metallic  magma. ' '  The  phrase 
"gas  of  any  kind"  is  important,  for,  although  he  generated  his  bub- 
bles of  gas  by  the  reaction  between  sulphuric  acid  and  the  carbonates 
of  the  gangue  or  between  the  acid  and  the  limestone  that  he  added  to 
the  pulp,  he  hit  upon  one  of  the  fundamental  principles  of  the  flotation 
process  as  we  know  it  now.  If  he  had  specified  air  as  the  particular 
gas  to  be  used  he  would  have  been  acknowledged  as  the  pioneer  of  pres- 
ent-day flotation.  Air  was  present,  of  course,  and  played  an  important 
part  in  the  operation,  for  in  his  description  he  specified  the  use  of  a 
centrifugal  mixing  device  "in  which  two  stirrers  work  in  opposite  di- 
rections, making  300  revolutions  per  minute*"  In  his  patent  he  ex- 
plained that  "the  sulphide  particles  when  moistened  by  a  fatty  sub- 
stance" have  a  tendency  "to  unite  as  spherules  and  to  float  upon  the 
surface  of  the  water."  He  stated  also  that  "the  rapidity  of  the  forma- 
tion of  the  spherules  and  their  ascension  is  in  direct  ratio  to  the  quan- 
tity of  gas  produced  in  a  given  time."  As  to  oil.  his  patent  mentions 
"a  thin  layer  of  ordinary  oil,"  but  in  the  instructions  given  by  him 
to  the  Minerals  Separation  people  he  specified  as  little  as  "1%  of  oil 
for  ore  containing  up  to  5%  of  metals"  and  up  to  3J%  "for  ore  con- 
taining 50%  of  metallic  lead." 

MINERALS  SEPARATION 

Before  proceeding  further  it  will  be  necessary  to  trace  the  origin 
of  Minerals  Separation,  Ltd.  At  the  end  of  1901,  John  Ballot,  W.  W. 
Webster,  and  James  Hay  formed  themselves  into  a  syndicate  to  take 
an  option  on  the  Australian  rights  to  the  Elmore  bulk-oil  process.  They 
engaged  the  firm  of  Sulman  &  Picard  to  act  as  advisory  metallurgists. 
Acting  on  their  advice,  the  syndicate  did  not  exercise  the  option.  In 
December  1902  John  Ballot  purchased  the  patents  of  Arthur  R.  Catter- 
mole  and  assigned  them  to  his  syndicate,  which  became  known  as  the 
Cattermole  Ore  Concentration  Syndicate.  On  December  31,  1903,  this 


20  FLOTATION 

syndicate  was  succeeded  by  a  company,  called  Minerals  Separation, 
Ltd.,  the  directors  being  John  Ballot,  J.  H.  Curie,  W.  W.  Webster,  S. 
Gregory,  H.  L.  Sulman,  and  H.  F.  K.  Picard. 

Now  we  return  to  Froment.  His  work  appears  to  have  been  un- 
known in  England  until  an  abstract  of  his  British  patent  was  pub- 
lished in  the  Journal  of  the  Society  of  Chemical  Industry  and  was  seen 
by  Mr.  Sulman  in  August  1903.  Whereupon  negotiations  for  the  pur- 
chase of  Froment 's  patent  were  opened  by  Mr.  Ballot.  He  went  to 
Milan  to  meet  Froment,  who,  on  November  7,  1903,  sold  his  rights  for 
£225.  On  December  29  Froment  sent  some  drawings,  with  descriptions 
and  instructions  explaining  his  mode  of  operation.  Early  in  1904  a 
small  plant  designed  by  him  was  forwarded  to  London,  but  the  appara- 
tus was  discarded,  and  destroyed  subsequently,  by  the  Minerals  Sep- 
aration people.  Froment  was  in  poor  health  at  that  time,  and  he  died 
soon  afterward.  His  patents  had  been  taken  out  in  Great  Britain  and 
Italy,  but  not  in  the  United  States,  and  when  Mr.  Ballot  acquired  them 
it  was  too  late  to  obtain  American  rights,  more  than  a  year  having 
elapsed  since  the  grant  of  the  British  patent,  on  June  9,  1902.  So  the 
Froment  patent  was  set  aside  as  of  no  immediate  value. 

Cattermole's  patents  had  been  duplicated  in  the  United  States.  In 
his  American  patent,  No  777,273  of  September  28,  1903,  Cattermole 
prefaces  his  description  by  reference  to  the  selectiveness  of  oil,  when 
emulsified,  for  sulphide  particles,  such  selective  action  being  intensified 
by  acidulation  of  the  water.  He  then  proceeds  to  say  that  if  the  mix- 
ture be  agitated  thoroughly  there  is  a  tendency  for  the  metalliferous 
particles,  now  well  coated  with  oil,  to  adhere  together,  forming  'gran- 
ules' that  sink  and  are  readily  separated  from  the  lighter  gangue  by 
an  up-current  of  water.  In  his  description  of  the  operation  he  says 
that  "the  granules,  with  a  certain  amount  of  heavy  sands,  sink  to  the 
bottom  and  are  discharged  (See  Fig.  1)  through  a  pipe  G1  into  the 
vessel  A5,  while  the  lighter  sands  are  carried  away  by  the  upward  cur- 
rent and  discharged  through  outlet  G2  to  a  light-sands  tank  J."  In 
the  drawing,  A1,  A2,  A3,  A4,  A5,  and  A6  are  mixing-vessels;  G  and  K 
are  classifiers;  E  is  a  tank  containing  oil-emulsion.  He  refers  to  the 
proportion  of  oil  several  times  in  vague  terms,  explaining,  however, 
that  it  should  be  insufficient  to  materially  lessen  the  specific  gravity  of 
the  metalliferous  mineral  particles. ' '  Finally,  he  specifies  the  propor- 
tion as  "usually  an  amount  of  oil  varying  from  4%  to  6%  of  the 
weight  of  metalliferous  mineral  matter  present  in  the  ore. ' '  This  can 
be  interpreted  variously ;  if  it  refers  to  the  sulphides  to  be  concen- 
trated, then  an  ore  containing  20%  blende  would  require  from  0.8  to 


THE    HISTORY   OF    FLOTATION 


21 


No.  763,259.  PATENTED  JUNE  21,  1904. 

A.  E.  CATTERMOLE. 
CLASSIFICATION  OF  THE  METALLIC  CONSTITUENTS  OF  ORES. 

APPLIOATIOK  FILED  SEPT.  39.  1(08. 
10  MODEL. 


!p 

*t 


_^r /cCtcAft,  ,^£ 

A^^ 


2%  of  oil,  or  from  16  to  24  Ib.  per  ton  of  ore.  On  the  other  hand,  a 
2%  chalcocite  ore  would  need  only  1.6  to  2.4  Ib.  of  oil  per  ton  of  ore, 
which  is  as  little  as  is  now  used.  Such  was  the  method  from  which 
patent  835,120  of  Minerals  Separation  is  claimed  to  be  a  logical  de- 
velopment. 

Much  of  the  early  experimental  work  of  Minerals  Separation  was 


22  FLOTATION 

done  in  the  laboratory  of  Sulman  &  Picard,  at  44  London  Wall,  but  in 
March  1904  Mr.  Ballot  established  his  own  laboratory  on  Alderman- 
bury  avenue,  and  it  was  there  that  decisive  results  were  obtained.  In 
1903  a  model  50-ton  plant,  to  use  the  Cattermole  process,  was  con- 
structed and  sent  to  the  Central  mine  at  Broken  Hill,  Australia. 

The  Minerals  Separation  people,  notably  the  chief  metallurgists, 
Messrs.  Sulman  &  Picard,  were  experimenting  with  Cattermole 's 
method  and  trying  to  develop  a  workable  process  at  the  time  when 
their  attention  was  called  to  Froment 's  patent.  When  they  acquired 
this  patent,  they  made  experiments  in  accord  with  the  specifications 
and  the  later  instructions  sent  by  Froment.  To  the  detached  spectator 
it  would  seem  more  logical  to  assume  that  Froment 's  floating  'spher- 
ules' rather  than  Cattermole 's  sinking  'granules'  would  lead  to  some- 
thing like  the  froth-flotation  process  of  today.  But  that  is  not  the 
story  told  in  the  courts  of  law.  The  metallurgists  identified  with  Min- 
erals Separation  testify  that  they  had  discarded  Froment 's  patent  and 
his  instructions,  having  found  them  worthless,  and  were  trying  vari- 
ous modifications  of  the  Cattermole  method  when  suddenly  they  hap- 
pened upon  the  particular  combination  essential  to  the  froth-agitation 
process.  Messrs.  Ballot,  Sulman,  and  Picard  agree  in  stating  that  pro- 
tracted experiments  were  being  conducted  in  their  London  laboratory 
under  the  immediate  charge  of  Arthur  H.  Higgins,  who  had  been  in- 
structed to  try  all  sorts  of  variations  in  temperature,  acidulation,  oil- 
ing, and  mixing.  Nothing  noteworthy  happened  until  the  proportion 
of  oil  was  reduced,  whereupon  the  'granules'  began  to  rise  instead  of 
sinking  and  "the  quantity  of  floating  material  increased  rapidly  when 
the  oil  was  reduced  below  a  certain  point,  this  point  being  0.62%  of  the 
oleic  acid  on  the  ore. ' '  So  testifies  Mr.  Ballot.  Thus  happened  ' '  the 
startling  discovery  of  the  agitation-froth  process,"  according  to  W.  H. 
Ballantyne,  Mr.  Ballot's  patent  lawyer.  The  date  was  March  3, 
1905.  Then  followed  the  British  patent  No.  7803  of  April  12,  1905, 
and  the  American  duplicate,  No.  835,120 — the  date  of  application 
being  May  29,  1905.  and  the  date  of  issue  November  6,  1905. 

Before  leaving  this  part  of  the  story  it  is  worth  noting  that  the  Cat- 
termole 50-ton  plant,  already  mentioned,  had  been  erected  in  the  Cen- 
tral mill  early  in  1904,  and  experiments  were  made  there  under  the  di- 
rection of  Gr.  A.  Chapman.  Tests  showed  that  when  using  0.75%  of  oil 
on  the  ore  "the  results  were  excellent,  with  all  float  concentrate,  no 
granular  material  being  formed. ' '  So  says  James  Hebbard,  the  man- 
ager of  the  Central  mine.15  The  adjective  "excellent"  is  used  in  the 


^Proceedings  Aust.  Inst.  of  M.  E.,  November  10,  1913.    The  same  engineer 


THE    HISTORY    OF    FLOTATION  23 

light  of  later  events,  for  floating  of  the  mineral  was  incompatible  with 
the  granulation  upon  which  the  Cattermole  process  depended.  The 
importance  of  the  floating  does  not  seem  to  have  been  appreciated  until 
a  year  later — early  in  1905 — when  "a  remarkable  development  in  the 
operation  was  discovered  (strangely  enough,  at  the  same  time  here 
[Central  mine]  and  in  the  Patent  Co.'s  [Minerals  Separation]  labor- 
atory in  London),  which  had  for  its  main  principle  the  reversal  of  all 
previous  operations,  and  consisted  in  the  complete  flotation  of  each 
particle  of  mineral  independently  in  place  of  granulating  the  mineral 
particles  and  causing  them  to  sink,  thus  not  only  revolutionizing  the 
process,  but  greatly  simplifying  and  cheapening  it.  The  developments 
noted  were  mainly  along  the  line  of  decreased  consumption  of  oleic 
acid,  for  example,  from  3%  oleic  on  ore,  resulting  in  very  little  float, 
down  to  l%,1(i  giving  practically  a  complete  float."  According  to  this, 
the  Higgins  'discovery'  was  made  independently  arid  contemporane- 
ously at  Broken  Hill,  but  the  underlying  principle  was  detected  a  year 
earlier  by  Mr.  Chapman,  who  had  experimented  with  the  Froment  pro- 
cess in  the  London  laboratory  of  Minerals  Separation  during  1903 — 
again  the  suggestion  that  Froment  had  pointed  the  way  to  the  agita- 
tion-froth process. 

Next  we  revert  to  the  first  contact  between  the  Elmore  brothers  and 
the  Minerals  Separation  people.  As  already  mentioned,  in  1901  the 
Ore  Concentration  Syndicate  gave  Messrs.  Ballot,  Webster,  and  Hay 
an  option  on  the  Australian  rights  to  the  Elmore  bulk-oil  process. 
In  accordance  with  this  agreement,  Mr.  Ballot  and  his  associates  sent 
ore  to  be  tested  at  the  Elmore  laboratory,  to  which  they  had  free  access 
while  the  experimentation  was  in  progress.  In  the  agreement  it  was 
stipulated  that  the  holders  of  the  option  "and  their  assigns"  should 
notify  the  Elmore  syndicate  of  any  "improvement,  addition,  or  dis- 
covery" that  they  might  make  and  the  Elmore  syndicate  was  "to  be 
entitled  to  every  such  improvement,  addition,  or  discovery  whether 
the  same  shall  be  patented  or  not. ' ' 

Mr.  Ballot  and  his  associates  made  tests  and  held  the  option  for  11 
months,  that  is,  until  late  in  1902.  Messrs.  Sulman  and  Picard  were 


relates  how,  before  1901,  "it  had  been  long  observed  that  a  froth  was  formed 
containing  high  metallic  values,  in  silver  and  lead  particularly,  whenever 
conditions  were  favorable,  as  for  instance,  where  the  rotation  of  trommels, 
or  the  splash  of  the  elevators  or  raff-wheels,  or  the  motion  of  the  jig-plungers, 
produced  a  violent  agitation  of  the  mill-water  containing  slime."  The  use 
of  oil  tended  to  make  such  froth,  more  persistent.  I  have  mentioned  the 
suggestion  made  by  Beauchamp  and  Shellshear  in  1902  while  at  work  in  this 
same  mill. 

below  1%,  apparently. 


24  FLOTATION 

engaged  by  Mr.  Ballot  to  supervise  the  tests.  They  were  ' '  treated  with 
the  greatest  frankness,"  says  Stanley  Elmore.  The  option  was  not  ex- 
ercised. Then  followed  Mr.  Ballot's  purchase  of  the  Cattermole  pat- 
ents and  in  the  succeeding  year  the  acquisition  of  the  Froment  and 
Sulman  &  Picard  patents,  followed  immediately  by  the  organization  of 
Minerals  Separation,  Ltd.,  as  a  process-exploiting  company.  In  1905 
the  Elmores  brought  suit  to  enforce  the  clause  above  quoted,  in  the 
agreement  of  1901,  claiming  that  they  were  entitled  to  the  benefit  of  the 
improvements  following  upon  the  insight  into  the  process  given  to  the 
Minerals  Separation  people  during  the  tests  made  under  the  option. 
The  case  went  against  the  Elmores,  the  Court  of  first  resort  deciding 
that  the  particular  clause  had  been  introduced  into  the  contract  with- 
out sufficient  authority  after  it  had  been  signed.  In  the  second  trial, 
Messrs.  Ballot,  Hay,  and  Webster  presented  evidence  to  show  that  the 
Cattermole  and  other  patents  had  never  been  in  their  possession  but 
had  passed  from  the  inventors  through  a  trustee  to  the  syndicate  that 
became  Minerals  Separation,  Ltd.  Whereupon  the  proceedings  were 
stayed.  The  affair  left  a  feeling  of  bitter  animosity  between  the  two 
factions ;  the  Elmores  showed  so  keen  a  sense  of  betrayal  as  to  resign 
from  the  Institution  of  Mining  and  Metallurgy  when  Mr.  Sulman  was 
nominated  for  the  presidency  of  that  professional  society  in  1911.  This 
incident  indicates  the  bitterness,  rather  than  the  merits  of  the  quarrel, 
but  it  must  be  recorded  in  this  history  of  the  process  because  it  helps 
to  explain  the  acerbity  of  the  litigation  that  ensued  and  that  still  ani- 
mates the  protagonists  in  this  metallurgical  vendetta. 

For  three  years,  from  1906  to  1909,  the  Elmores  fought  the  Min- 
erals Separation's  attempt  to  hold  a  patent  in  Germany.  The  patent 
was  granted,  but  it  was  annulled  subsequently  by  a  higher  court. 

In  1907  Minerals  Separation  brought  suit  against  the  Ore  Concen- 
tration Company,  alleging  infringement  of  Froment 's  patent,  but  in 
1909  the  Minerals  Separation  company  discontinued  the  action,  pay- 
ing costs. 

In  1909  the  Elmores  and  the  British  Ore  Concentration  Syndicate 
brought  suit  against  Minerals  Separation  for  infringement  of  Frank 
Elmore 's  bulk-oil  patent  of  1898  and  Stanley  Elmore 's  patent  of  1901, 
specifying  the  use  of  acid  in  the  bulk-oil  process.  They  lost  in  the  first 
court,  they  won  on  appeal,  but  lost  on  final  resort  to  the  House  of 
Lords.  Both  the  use  of  oil  and  of  acid  were  held  to  have  been  antici- 
pated, and  the  Minerals  Separation  froth-agitation  process  was  held 
to  be  entirely  different  from  the  bulk-oil  method.  Subsequently  a 
new  suit  was  started  in  Australia,  the  claim  of  infringement  against 


THE   HISTORY    OF    FLOTATION  25 

the  Sulphide  Corporation,  a  licensee  of  Minerals  Separation,  being 
based  on  acidulation.  The  Australian  court  decided  against  the 
Elmores,  who  appealed,  unsuccessfully,  to  the  Privy  Council,  in  1914. 

AIR-AGITATION    METHODS 

It  is  important  to  note  that  these  suits  dealt  only  with  the  bulk-oil 
patents  of  1898  and  1901,  and  had  no  reference  to  the  vacuum  process 
of  1904.  To  the  agency  of  gas  in  flotation  we  now  return.  So  far  the 
fact  that  bubbles  of  air  would  do  the  work  of  bubbles  of  chemically  gen- 
erated gases  had  been  overlooked.  In  September  1903,  Sulman  &  Pic- 
ard  described  the  use  of  air  "or  other  gas"  in  British  patent  No.  20,- 
419,  which  was  duplicated  in  the  United  States  as  No.  793,808.  In 
this  they  pictured  a  perforated  coil  of  pipe  through  which  either  air 
is  introduced  into  pulp  with  which  oil  has  been  already  mixed  or  air 
and  oil  are  admitted  simultaneously  in  the  form  of  a  spray.  The  lat- 
ter scheme  has  not  proved  practicable,  whereas  the  procedure  in  which 
the  oil  is  previously  mixed  with  the  pulp  and  then  subjected  to  aeration 
by  the  introduction  of  air  through  the  perforations  in  the  pipe  is  a 
practical  method.  They  said,  "The  oiled  metalliferous  particles  re- 
sulting from  either  of  the  processes  above  described  have  the  power  of 
attracting  to  themselves  with  a  greater  comparative  strength  than  the 
gangue  particles,  the  films  or  bubbles  of  gas  which  exist  in  the  mass  and 
are  thus  raised  to  the  surface  of  the  liquor  by  gaseous  flotation.''  They 
did  not  claim  the  use  of  air  as  a  discovery  and  they  seem  not  to  have 
known  how  near  they  were  to  the  later  phase  of  flotation,  in  which  the 
making  of  a  multiplicity  of  air-bubbles,  or  '  froth ',  is  the  principal  fea- 
ture. 

In  June  1904  Frank  Elmore  applied  for  a  patent  to  use  electrolysis 
in  order  to  generate  gas  in  a  freely  flowing  pulp,  and  in  August  of  the 
same  year  he  obtained  British  patent  No.  17,816,  in  which  he  described 
the  performance  of  flotation  in  a  vacuum,  so  as  to  liberate  "the  air  or 
gases  in  the  milling  water. ' '  Thus  six  years  after  the  date  of  his  first 
bulk-oil  patent  Elmore  had  learned  to  put  the  air  to  purposeful  use. 
He  subjected  the  oiled  and  acidulated  pulp  to  a  vacuum,  thereby  re- 
leasing the  2.2%  of  air  normally  absorbed  in  water.  By  lowering  the 
pressure  and  raising  the  temperature  this  air  is  released,  thereupon 
attaching  itself,  in  the  form  of  bubbles,  to  the  oiled  sulphide  particles, 
which  rise  to  the  surface.  For  example,  the  air  in  a  ton  of  pulp  con- 
sisting of  6  parts  of  water  to  1  of  ore  suffices  to  lift  360  pounds  of  zinc- 
lead  sulphides  in  a  Broken  Hill  ore.  In  actual  practice,  however,  the 
weight  of  sulphides  floated  is  considerably  greater  than  the  theoretical 


26  FLOTATION 

proportion  as  based  on  the  efficacy  of  the  air  released  from  absorption 
in  water.  Part  of  the  work  is  done  by  the  gaseous  carbon  di-oxide 
liberated  by  the  reaction  between  the  acid  and  the  carbonates,  such  as 
calcite,  either  in  the  gangue  or  added  in  the  form  of  limestone.  But  a 
larger  part  of  the  bubbling  is  caused  by  the  air  entangled  in  the  ore 
particles  and  entrained  in  the  pulp  during  energetic  mixing.  In  this 
process  the  quantity  of  oil  added  to  the  pulp  was  reduced  from  the  ton 
used  at  Glasdir  to  10  pounds  per  ton  of  ore.  and  finally  to  as  little  as 
3  pounds  per  ton  of  ore.  The  machine  devised  by  Mr.  Elmore  for  the 
performance  of  his  vacuum  process  was  remarkably  ingenious  and  to 
it  the  success  of  the  process  was  largely  due.  It  was  applied  at  several 
Scandinavian  copper  mines,  notably  the  Sulitelma,  and  also  in  the 
Zinc  Corporation's  mill  at  Broken  Hill,  as  already  mentioned. 

This  vacuum  method  of  Elmore  was  a  notable  step  toward  the  rec- 
ognition of  the  part  played  by  air  in  flotation,  and  in  so  far  as  he  used 
air  in  a  pulp  that  had  undergone  agitation  with  a  relatively  small  pro- 
portion of  oil  he  furnished  a  metallurgic  sign-post  that  pointed  to  the 
final  success  of  the  process. 

FLOTATION    IN    AMERICA 

So  far  flotation  had  received  scant  attention  in  the  United  States. 
The  old  Elmore  bulk-oil  method  had  been  tried,  unsuccessfully,  at  the 
Boston  Consolidated  and  Mammoth  mines  in  Utah  in  1900  and  1901. 
In  1906  a  surface-tension  process  of  great  ingenuity,  invented  by  A.  P. 
S.  Macquisten,  was  used  in  the  Adelaide  mill,  at  Golconda,  Nevada,  and 
in  1911  a  similar  plant  was  erected  at  the  Morning  mine,  in  Idaho,  but 
these  interesting  efforts  were  mere  ripples  on  the  calm  surface  of  Amer- 
ican apathy,  which  at  the  time  gave  no  promise  of  the  full  tide  of  met- 
allurgical advance  that  since  then  has  swept  over  base-metal  mining  in 
the  West. 

Another  American  patent  must  be  mentioned,  as  linking  the  El- 
more bulk-oil  process  with  the  later  frothing  methods.  The  patent  of 
Edmund  B.  Kirby  is  No.  809,959  of  December  14,  1903.  He  used  from 
25  to  75%  of  oil  in  a  flowing  pulp ;  but  he  depended  upon  thin  oil — 
kerosene — and  violent  agitation,  so  that  he  departed  from  the  Elmore 
type  of  flotation.  The  more  interesting  feature  of  his  claim,  however, 
is  "the  injection  of  a  gas,  preferably  air,  into  the  mass, "  which  state- 
ment, if  taken  with  his  reference  to  "allowing  the  hydrocarbon-coated 
particles  to  float  to  the  surface  of  the  mass, ' '  seems  indeed  to  be  a  fore- 
cast of  froth-flotation.  The  patentee — Kirby — himself  says:  "It  is 
thought  that  the  use  of  a  gas  to  assist  in  the  flotation  of  the  coated 


THE    HISTORY    OF    FLOTATION  27 

particles  *  *  *  is  radically  new  in  this  art. ' '  He  adds :  * '  The  employ- 
ment of  the  gas  in  the  manner  stated  brings  in  a  more  powerful  floating 
agency  than  anything  before  used. ' '  How  prophetic !  His  gas  was 
"preferably  air."  Moreover,  he  knew  of  the  use  to  be  made  of  the  air 
•"dissolved"  in  water,  as  adopted  a  year  later  by  Francis  E.  Elmore, 
for  he  says:  "The  air-bubbles  not  only  tend  to  attach  themselves  di- 
rectly to  the  coated  particles,  and  thus  float  them  to  the  surface,  but 
the  air  becomes  dissolved  in  the  water  to  its  maximum  capacity.  This 
dissolved  air  tends  to  again  separate  itself  from  the  water  and  attach 
itself  in  minute  globules  to  the  coated  particles. ' '  Mr.  Kirby  tried  his 
process  on  a  number  of  British  Columbian  ores,  but  no  working  plant 
was  erected;  nevertheless,  it  is  apparent  that  he  has  not  received 
proper  credit  hitherto  for  his  ingenuity,  and  it  is  a  pleasure  to  make 
the  correction  here.  . 

The  credit  for  bringing  the  froth  process  to  the  notice  of  the  Amer- 
ican public  belongs  to  J.  M.  Hyde,  who  had  been  in  the  employ  of  a  sub- 
sidiary syndicate  organized  by  Minerals  Separation  for  the  exploitation 
of  flotation  in  Mexico.  Mr.  Hyde  was  introduced  to  Mr.  Ballot  by  The- 
odore J.  Hoover,  who,  in  October  1906,  had  been  engaged  by  Mr.  Ballot 
as  technical  adviser  and  general  manager  for  the  Minerals  Separation 
company.  In  1910  Mr.  Hyde  went  to  Mexico  and  early  in  1911  he  re- 
signed, at  the  conclusion  of  his  one-year  contract  with  the  syndicate. 
Shortly  afterward  he  went  to  Montana,  at  the  instance  of  H.  C.  Hoov- 
er, to  inspect  the  property  of  the  Butte  &  Superior  Copper  Co.,  this 
company  having  offered  Mr.  Hoover  a  participation  in  a  bond  issue. 
The  business  proving  unattractive,  Mr.  Hoover  withdrew  from  it,  but 
Mr.  Hyde  commenced  to  investigate  the  metallurgical  problem  pre- 
sented by  the  zinc-lead  ore  of  the  Butte  &  Superior  company's  Black 
Rock  mine.  After  making  the  necessary  tests  with  the  slide  machine, 
he  erected  a  trial  plant  in  disregard  of  the  Minerals  Separation  pat- 
ents. This  was  in  August  1911,  and  not  until  the  Butte  &  Superior 
company  had  negotiated  with  E.  H.  Nutter,  the  American  manager  for 
Minerals  Separation,  who  demanded  a  prohibitive  royalty.  In  October 
1911  suit  for  infringement  of  patent  was  brought  by  Minerals  Separa- 
tion against  Mr.  Hyde. 

Meanwhile,  in  December  1910,  T.  J.  Hoover  had  severed  his  connec- 
tion with  Minerals  Separation,  after  having  been  instrumental  in  the 
successful  development  of  the  company's  business  in  Australia  and  in 
improving  the  various  apparatus  employed  in  the  froth-flotation  pro- 
cess, especially  in  that  country.  His  resignation  was  accompanied  by 
some  friction  with  Mr.  Ballot,  into  the  details  of  which  it  is  not  neces- 


28  FLOTATION 

sary  to  go,  but  the  fact  is  a  part  of  the  history  of  the  process.  In  De- 
cember 1912  Mr.  Hoover  published  his  book,  'Concentrating  Ores  by 
Flotation, '  after  a  grudging  consent  had  been  obtained  from  his  former 
employers,  in  return  for  which  he  excised  parts  of  the  original  manu- 
script trenching  too  deeply  into  patent  matters.  This  is  recorded  here' 
in  order  to  remove  the  impression,  still  persisting,  that  Mr.  Hoover 
wrote  and  published  his  book  while  connected  with  Minerals  Separa- 
tion.17 

We  now  return  to  Mr.  Hyde  and  the  commencement  of  a  big  litiga- 
tion. The  suit  started  against  him  in  1911  was  tried  first  in  the  Dis- 
trict Court  of  Montana  and  judgment  was  given  against  him  in  August 
1913.  On  appeal,  before  the  U.  S.  Circuit  Court  of  San  Francisco,  this 
judgment  was  reversed  in  May  1914.  By  writ  of  certiorari  the  case 
was  brought  before  the  Supreme  Court  of  the  United  States,  which  on 
December  11,  1916,  reversed  the  decision  of  the  Appellate  Court  and 
decreed  that  patent  835,120  was  valid,  but  confined  the  scope  of  the 
patent  to  violent  mechanical  agitation,  the  use  of  less  than  1%  of  oil, 
and  a  persistent  kind  of  froth. 

It  is  worthy  of  note  that  the  first  successful  froth-flotation  plant 
erected  in  the  United  States,  by  Mr.  Hyde  in  1911,  did  not  start  until 
six  years  after  the  grant  of  patent  835,120  and  not  until  20%  of 
the  world's  production  of  zinc  was  being  made  by  aid  of  the  group 
of  other  flotation  processes  in  use  at  Broken  Hill.  This  may  be 
compared  with  the  statement  of  the  U.  S.  Supreme  Court,  in  its  final 
review  of  the  Hyde  case,  that  * '  the  process  in  suit  promptly  came  into 
extensive  use  for  the  concentration  of  ores  in  most,  if  not  all,  of  the 
principal  mining  countries  of  the  world,  notably  in  the  United  States. ' ' 

The  first  successful  application  of  the  froth-flotation  process  in  the 
United  States  was  made  at  Butte,  on  a  zinc-lead  ore,  as  we  have  seen. 
The  later  development  of  the  process  has  been  based  on  the  treatment 
of  copper  ores,  especially  the  chalcocite  disseminated  in  the  immense 
orebodies  disclosed  in  Arizona,  Utah,  and  Nevada.  This  part  of  the 
story  begins  with  the  tests  made  by  Minerals  Separation  in  their  Lon- 
don laboratory  and  in  plants  erected  at  sundry  copper  mines  in  other 
countries,  such  as  the  Caucasus  Copper  and  the  Great  Fitzroy,  with  re- 
sults generally  poor.  In  his  book,  dated  July  4,  1912,  Mr.  Hoover  re- 


i7ln  mentioning  these  and  other  personal  incidents,  like  the  Elmore-Sul- 
man  &  Picard  affair,  I  am  prompted  solely  by  the  desire  to  state  facts  essen- 
tial to  a  correct  understanding  of  the  conditions  governing  the  patent  litiga- 
tion, because  they  played  a  decisive  part  in  the  technical  development  of  the 
process. 

is'Concentrating  Ores  by  Flotation,'  first  edition,  page  157. 


'THE   HISTORY   OF   FLOTATION  29 

fers  to  the  limitations  of  the  process  and  says:18  "The  fourth  limita- 
tion is  one  for  which  at  present  no  adequate  reason  can  be  given.  An 
ore  in  which  the  valuable  minerals  are  wholly  or  partly  bornite  or 
chalcocite,  as  those  of  Bingham  canyon,  will  probably  give  trouble  to 
flotation  processes,  although  not  always,  for  among  the  many  ores 
tested  the  one  which  gave  the  most  uniformly  satisfactory  results  was  a 
copper  ore  assaying  2.8%  copper,  all  in  the  form  of  microscopic  specks 
of  bornite."  He  proceeds  to  remark:  "It  may  be  that  only  those  ores 
where  bornite  and  chalcocite  are  of  secondary  occurrence  give 
trouble."  In  Mr.  Hyde's  report  of  January  8,  1911,  given  as  an  ex- 
hibit in  the  lawsuit,  it  is  stated  that  the  tests  carried  out  in  the  Minerals 
Separation  laboratory  proved  that  "the  copper  ores  of  a  good  part  of 
the  Southwest  and  also  of  at  least  a  portion  of  the  Utah  region  contain 
chalcocite,  ivhich  is  not  floatable  by  any  of  the  methods  so  far  tested." 
This  summarizes  the  opinion  held  by  the  Minerals  Separation  staff  at 
that  time.  However,  they  discovered  their  mistake  two  years  later. 
Tests  on  chalcocite  ore  from  the  Inspiration  mine,  in  Arizona,  were 
made  in  Mr.  Nutter's  laboratory  at  San  Francisco  during  1912,  but 
the  results  were  not  good  enough.  At  the  end  of  that  year,  however,  an 
87%  recovery  on  a  2%  copper  ore  was  obtained  in  a  15%  concentrate. 
The  telegram  sent  to  the  New  York  office  of  the  company  was  mutilated 
in  transit  so  as  to  state  that  a  50%  concentrate  had  been  obtained,  and 
premature  rejoicing  followed.10  Nevertheless  the  Minerals  Separation 
staff  promised  good  results  and  erected  a  50-ton  experimental  plant  at 
the  Inspiration  mine.  The  company  took  out  a  license  early  in  1913. 
On  March  23  an  experiment  on  low-grade  chalcocite  ore  was  made  by 
T.  A.  Janney  at  the  Arthur  mill  of  the  Utah  Copper  Company.  This 
proved  satisfactory.  During  that  same  month,  March  1913,  the  Miner- 
als Separation  staff,  at  the  Inspiration  mine,  had  demonstrated  a  90 
to  92%  recovery  and  a  35  to  40%  concentrate  on  a  2%  ore,  with  a  0.15 
to  0.2%  tailing.  The  presence  of  a  colloidal  kaolinized  mineral  diverted 
the  oil  from  its  proper  function  and  interfered  with  the  recovery 
of  copper  until  G.  A.  Chapman  suggested  the  addition  of  the  oil  to  the 
ore  in  the  tube-mill,  where  the  metallic  particles  became  oiled  at  the 
instant  of  exposing  fresh  fractures.  These  experiments  warranted  the 
expectation  that  on  a  1.58%  ore  there  would  be  obtained  a  27|%  con- 
centrate with  a  recovery  of  92%  and  a  tailing  loss  of  only  0.13%.  A 
600-ton  Minerals  Separation  test-plant  was  erected  in  January  1914; 
in  July  of  that  year  a  pneumatic  equipment  consisting  of  five  Callow 
cells  and  one  Pachuca  tank  was  added  and  between  August  and  Oc- 


S.  P.,  March  18,  1916. 


30  FLOTATION 

tober  a  Towne  machine  was  in  use.  In  1915  the  Inspiration  Consoli- 
dated Copper  Co.  built  a  mill  of  18  sections,  each  of  800  tons  capacity, 
or  a  total  of  14,400tons  daily.  Since  then  this  mill  has  treated  as  much 
as  21,000  tons  in  a  day. 

In  June  1914  Mr.  Chapman  started  flotation  experiments  at  Ana- 
conda in  a  200-ton  plant,  obtaining  90%  recovery.  On  February  1, 
1915,  the  Anaconda  and  Inspiration  companies  signed  a  contract  with 
Minerals  Separation  by  the  terms  of  which  they  agreed  to  pay  royalty 
on  a  sliding  scale  ranging  from  12  cents  per  ton  on  4000  tons  daily  to 
4  cents  per  ton  on  the  treatment  of  more  than  30,000  tons  daily.  By 
a  curious  proviso  in  the  contract  no  royalty  was  payable  on  the  5000 
tons  between  10,000  and  15,000  tons  daily.  The  tonnage  coming  under 
the  terms  of  this  agreement  included  the  ore  treated  by  sundry  sub- 
sidiary companies,  the  consequence  being  that  the  maximum  tonnage 
and  minimum  royalty  specified  in  the  agreement  were  reached  by  the 
close  of  1916  at  which  time  the  Anaconda  flotation  plant  was  treating 
14,400  tons  daily.  As  an  example  of  the  saving  made  by  aid  of  flota- 
tion, it  is  worth  mentioning  that  whereas  the  tailing  from  the  water- 
concentration  mill  used  to  assay  0.62%  copper,  the  residue  now  after 
treatment  in  the  flotation  annex  assays  only  0.15%  on  a  3%  ore;  that 
is,  out  of  60  pounds  of  copper  per  ton  only  3  pounds  goes  to  waste,  as 
compared  with  12.4  pounds  formerly.  The  recovery  is  95%.  More- 
over, the  metallurgical  improvements  made  at  the  Washoe  plant  during 
1915  were  so  effective  as  to  enable  an  increase  of  55.000,000  pounds 
per  annum  to  be  made  in  the  production  of  the  Anaconda  company 
"without  increasing  the  tonnage  or  grade  of  ore  that  has  been  mined 
in  the  past/'  So  testified  Mr.  John  D.  Ryan,  the  president  of  the  com- 
pany, in  his  annual  report.20  Further,  he  stated  that  "approximately 
40,000,000  pounds  of  this  increased  production  will  be  made  without 
adding  to  the  cost  per  ton  of  ore  treated."  This  is  the  equivalent  of 
the  output  from  a  big  mine. 

Meanwhile  preliminary  tests  had  been  started  at  the  Miami  mine, 
which  is  a  near  neighbor  of  the  Inspiration.  From  December  1913  to 
August  1914  the  testing  was  directed  by  R.  C.  Canby,  who  used  vari- 
ous types  of  apparatus,  notably  the  Minerals  Separation  and  Towne 
machines.  On  August  7,  1914,  a  pneumatic  flotation  plant  was  erected. 
The  remodeled  mill,  having  a  capacity  of  4200  tons,  went  to  work  on 
March  15,  1915.  On  July  14,  1914,  Minerals  Separation  brought  two 
separate  suits  based  on  patents  835,120  and  962,678,  but  these  suits 
were  dismissed  on  request  of  Minerals  Separation,  and  on  October  10, 


2QM.  &  S.  P.,  February  26,  1916. 


THE    HISTORY    OP    FLOTATION  31 

1914,  a  single  suit  was  started  for  infringement  of  three  patents,  the 
two  already  mentioned  and  No.  1,099,699. 

Instead  of  using  the  blade-impeller  type  of  agitator,  the  Miami  Cop- 
per Company  adopted  the  Callow  machine,  essentially  a  sloping 
launder  with  a  canvas  bottom  through  the  pores  of  which  air  under 
small  pressure  is  admitted  into  the  pulp  previously  oiled.  Such  oiling 
of  the  pulp  was  aided  at  first  by  the  use  of  a  Pachuca  tank,  but  in  the 
spring  of  1915  this  type  of  agitator  was  found  superfluous  and  since 
then  the  oil  has  been  simply  added  to  the  pulp  while  flowing  through 
a  launder  to  the  flotation-cell.  In  the  trial  of  the  suit  before  the  Dis- 
trict Court  of  Delaware,  the  defendant  claimed  that  he  was  not  using 
the  agitation-froth  process  of  patent  835,120  but  a  bubble  method  sim- 
ilar to  that  of  patent  793,808,  which  was  granted  to  Sulman  &  Picard 
on  July  4,  1905,  on  an  application  dated  October  5,  1903.  In  this  pat- 
ent a  perforated  coil  of  pipe  is  described,  the  idea  being  to  admit  air 
and  oil  in  the  form  of  spray,  so  that  the  globules  of  oil  attach  them- 
selves to  the  metallic  particles  in  the  ore  and  float  them  to  the  surface. 
The  pneumatic  machine  used  at  Miami  was  devised  by  J.  M.  Callow 
and  patented  as  No.  1,104,755  of  July  21,  1914.  The  idea  had  been 
used  already  in  T.  J.  Hoover's  British  patent  No.  10,929  of  1910.  Mr. 
Hoover's  patent  was  not  duplicated  in  the  United  States  and  Mr.  Cal- 
low was  unaware  of  it.  Another  investigator,  R.  S.  Towne,  had  pat- 
ented the  idea  previously,  in  the  form  of  a  carborundum  wheel,  the 
central  hole  of  which  he  plugged,  so  that  the  wheel  served  as  a  porous 
medium.  The  admission  of  air  to  make  froth,  without  the  aid  of  me- 
chanical agitation,  was  developed  in  several  machines  at  a  later  date — 
in  1915  and  1916 — as  has  been  duly  recorded  in  the  technical  press.21 
The  kind  of  froth  produced  by  blowing  bubbles  of  air  through  the  pulp 
is  claimed  to  be  different  from  that  made  by  beating  air  into  the  pulp 
with  a  mechanical  stirrer;  in  the  one  case  the  froth  is  said  to  be  thin, 
tender,  and  evanescent  while  in  the  other  the  froth  is  described  as  thick, 
coherent,  and  persistent. 

However,  the  first  trial-court  decided  in  favor  of  Minerals  Separa- 
tion's contention  that  the  Miami  Copper  Company  was  infringing  its 
patent,  835,120,  and  also  962,678.  The  judgment  was  delivered  on 
September  30,  1916,  an  appeal  being  filed  at  once  by  the  defendant. 


Kraut-Kollberg  Flotation  Machine.'  By  Max  Kraut,  M.  &  S.  P., 
July  1,  1916.  'An  Improved  Pneumatic  Flotation  Machine.'  By  James  M. 
Hyde,  M.  &  S.  P.,  November  25,  1916.  'The  Porous  Bottom.'  By  Rudolf  Gahl, 
M.  &  S.  P.,  September  30,  1916.  'Flotation  in  the  Clifton-Morenci  District.'  By 
David  Cole,  M.  &  S.  P.,  October  14,  1916.  'Flotation  at  the  Calaveras  Copper 
Mine.'  By  Hallet  R.  Robbins,  M.  &  S.  P.,  November  25,  1916. 


32  FLOTATION 

Patent  No.  962,678  is  important  and  interesting  because  it  involves 
an  idea  to  which  no  reference  has  as  yet  been  made  in  this  brief  history 
of  the  process:  I  refer  to  the  varying  solubility  of  oils  and  the  use  of 
soluble  agents  for  that  modification  of  the  surface-tension  of  water  to 
which  the  phenomena  of  froth-flotation  or  bubble-levitation  are  so 
largely  due.  The  idea  is  not  recent.  Haynes,  in  his  British  patent 
of  1860,  used  coal-tar  from  gas-works  in  a  rudimentary  process  of  oil- 
flotation.  Coal-tar  contains  as  much  as  20%  soluble  products.  In  U. 
S.  patent  788,247,  dated  April  25,  1905,  Cattermole,  Sulman,  and  Pi- 
card  used  cresol  and  phenol,  both  soluble  in  water,  as  modifying  agents. 

On  June  29,  1910,  Sulman  &  Picard  obtained  U.  S.  patent  962,678 
for  a  '* '  soluble  frothing  agent, ' '  and  this  is  the  patent  that  the  Miami 
company  is  charged  with  having  infringed  by  reason  of  using  cresol 
with  pine-oil  in  its  flotation  operations.  Application  for  this  patent 
was  filed  on  April  30,  1909.  The  illustration  shows  a  beater  form  of 
agitator  and  "beating  air  into  the  mixture"  is  specified.  Mention  is 
made  of  "an  organic  compound  in  solution"  and  "amyl  acetate"  is 
instanced.  No  particular  proportion  of  this  "mineral  frothing  agent" 
is  specified  and  an  increase  of  the  soluble  substance  is  held  not  to  inter- 
fere with  the  operation.  The  decision  of  the  higher  court  on  the  valid- 
ity of  this  patent  will  have  an  important  bearing  on  the  future  of  the 
flotation  process,  for  it  is  manifest  that  the  term  'soluble  frothing 
agent'  is  extremely  comprehensive  and  will  frustate  legitimate  at- 
tempts to  avoid  the  embargo  on  the  use  of  oil.  Meanwhile  the  Supreme 
Court's  recent  decision  validating  the  patent  on  the  use  of  a  'critical' 
proportion  of  oil,  namely  less  than  1%,  has  been  stultified  by  successful 
concentration  on  a  scale  of  1000  tons  or  more  per  day  when  using  22  to 
23  pounds  of  oil  per  ton  of  ore.  At  the  same  time  comes  the  news  of 
the  Freeman  process,  in  which  soda-cake  is  being  used  successfully  at 
Broken  Hill  as  a  modifying  agent  instead  of  oil.  The  litigation  is  far 
from  ended  and  before  it  is  closed  it  will  be  likely  that  oil  will  have 
been  discarded  in  favor  of  other  contaminants  capable  of  lowering  the 
surficial  tension  of  water  so  as  to  permit  the  formation  of  a  metallugic 
froth. 

In  1914  the  flotation  of  oxidized  lead  ores  became  the  subject  of  suc- 
cessful experiment,  the  method  being  to  sulphidize  the  exterior  of  the 
oxides  by  means  of  sodium  sulphide.  This  was  accomplished  so  success- 
fully that  an  effort  was  made  in  1915  to  apply  the  method  to  oxidized 
copper  ores,  which,  however,  are  not  readily  amenable  because  the  sul- 
phidization  penetrates  the  ore-particles  so  deeply  as  to  interfere  with 
the  differential  treatment  and  to  consume  an  excessive  amount  of  the 


THE    HISTORY    OF    FLOTATION  33 

sulphidizing  agent.  The  treatment  of  zinc-carbonate  ores  by  sulphide- 
filming  has  been  even  less  successful,  owing  to  the  fact  that  such  ores 
contain  enough  zinc  silicate  to  interfere  with  flotation. 

The  story  of  flotation  flows  by  devious  ways  and  is  broken  by  many 
cross-currents.  Patents  serve  to  record  the  high-water  marks  of  inge- 
nuity but  they  fail  to  disclose  the  movement  between  given  points,  and, 
what  is  much  more  important,  they  ignore  the  slow  increase  of  manipu- 
lative skill.  It  is  to  manipulation,  learned  empirically  in  the  labora- 
tory and  mill,  that  the  flotation  process  owes  its  metallurgic  success. 
Given  the  directions  to  be  found  in  Kirby's  or  Froment's  patents,  the 
flotation  expert  of  today  can  produce  an  effective  result,  without,  ap- 
parently, borrowing  from  any  later  inventor.  That  is  why  the  experi- 
ments made  in  Court  have  proved  almost  anything  it  was  desired  to 
prove.  The  manipulation  to  which  success  in  the  mill  is  largely  due 
contravenes  no  patent  and  trespasses  no  man's  preserves.  A  proof  of 
this  is  to  be  found  not  only  in  the  slow  application  of  the  flotation  idea 
.in  metallurgy  but  in  the  delay  that  marked  the  fruitful  use  of  the  latest 
phase  of  the  process.  The  froth-flotation  that  is  claimed  to  be  a  new 
discovery  is  said  to  have  been  discovered  in  1905 ;  yet  it  was  not  intro- 
duced into  an  American  mill  until  1911,  and  even  after  that  event  the 
most  skilful  engineers,  whether  in  the  employ  of  the  patent-mongering 
company  or  not,  failed  to  apply  it  successfully  for  several  years,  not 
until  1914. 

Haynes  and  Bradford  left  no  trail.  Everson  failed  to  arrive,  but  it 
is  likely  that  her  patent  put  the  idea  of  flotation  into  the  heads  of 
others,  for  example,  Robson.  He  did  not  succeed,  but  he  gave  the  clue 
to  Elmore,  who  then  prompted  Froment  and  Kirby.  Sulman  was  ex- 
perimenting with  the  Cattermole  method  when  he  heard  of  Froment's 
scheme,  and  from  that,  I  believe,  he  got  the  notion  of  using  air  to  make 
a  froth.  Hoover,  Callow,  and  other  technicians,  by  the  patient  empiri- 
cism of  the  mill  and  laboratory,  developed  a  workable  process.  Such, 
in  brief,  I  believe  to  be  the  true  pedigree  of  the  flotation  process. 


34  FLOTATION 

PRINCIPLES  OF  FLOTATION 

BY  T.  A.  RICKARD 
(From  the  Mining  and  Scientific  Press  of  July  7  and  14,  1917) 

INTRODUCTION.  The  understanding  of  the  principles  governing 
flotation  has  been  delayed  mainly  because  the  explanation  of  the  phe- 
nomena— or  appearances — characteristic  of  the  process  is  to  be  found 
in  physics  rather  than  in  chemistry.  Modern  metallurgy  has  been  in 
the  hands  of  men  primarily  chemists,  rather  than  physicists.  Cyanida- 
tion  and  chlorination,  for  example,  may  be  explained  by  chemical 
formulas,  even  if  they  cannot  be  expressed  in  their  entirety  by  the 
language  of  elemental  symbols;  but  flotation  is  not  to  be  interpreted 
in  that  way ;  it  is  controlled  by  physical  laws  that  are  obscure  and 
that  hardly  came  within  the  cognizance  of  the  metallurgist  until  the* 
need  for  study  was  felt  by  him  within  a  period  so  recent  that  the  full 
results  of  scientific  research  are  not  yet  available. 

To  understand  the  rationale  of  the  flotation  process  we  must  return 
to  the  amusements  of  our  boyhood;  in  the  soap-bubble  and  in  the 
greased  needle  we  shall  find  an  inkling  of  the  forces  at  play  in  the 
flotation  machine.  Everybody  knows  the  trick  of  the  greased  needle. 
If  a  needle  be  greased  and  then  placed  carefully  on  the  surface  of  tap- 
water  in  a  bowl  it  will  float,  despite  the  fact  that  steel  is  eight  times 
heavier  than  water.  Even  the  natural  oil  on  the  fingers,  or  that 
obtainable  by  passing  the  fingers  through  the  hair,  will  suffice  for  the 
purpose  of  assisting  the  needle  to  float. 

The  first  idea  is  that  the  buoyant  effect  of  the  oil  adhering  to  the 
needle  prevents  it  from  being  drowned.  However,  the  quantity  of  oil 
thus  attached  to  the  needle  is  not  enough  to  buoy  it ;  the  specific  gravity 
of  the  oil  is,  say,  0.9  as  compared  with  water,  which  is  the  unit  of 
specific  gravity;  therefore  the  flotative  margin  is  only  one-tenth,  and 
for  the  oil  to  float  a  piece  of  steel,  having  a  specific  gravity  of  8,  its 
volume  would  have  to  be  more  than  70  times  that  of  the  steel.  So  the 
buoyancy  of  the  oil  does  not  do  it.  Moreover,  an  ungreased  needle 
also  will  float.  This  experiment  must  be  conducted  carefully.  To  be 
certain  that  the  needle  was  free  from  grease1  I  held  it  in  metallic 
pincers,  dipped  it  in  a  solution  of  washing-soda  (sodium  carbonate, 


iNew  needles  are  slightly  greasy,  as  I  ascertained  by  means  of  the  camphor 
test,  described  later.     The  grease  protects  the  N  needles  from  rusting. 


PRINCIPLES   OF    FLOTATION  35 

which  is  a  solvent  for  grease),  and  then  dried  it,  taking  care  to  use  a 
clean  cloth  and  not  to  touch  it  with  my  fingers.  Then  I  placed  a  piece 
of  tissue-paper  on  the  water  in  a  cup  and  laid  the  needle,  held  in  the 
pincers,  upon  the  paper,  which  was  depressed  gently  into  the  water 
by  the  point  of  a  wooden  match,  until  the  paper  became  soggy  and 
finally  sank,  leaving  the  needle  floating.  It  lay  in  a  depression  of  the 
water-surface,  which  appeared  to  be  bent  under  it. 

The  needle  that  will  float  after  being  greased  is  larger  than  the 
one  that  floats  without  being  greased,2  so  the  oil  seems  to  aid  flotation ; 
but  when  the  needle  is  too  large  it  cannot  be  made  to  float,  greased  or 
not.  It  is  too  heavy ;  that  is,  the  force  of  gravity  multiplied  by  mass 
is  sufficient  to  overcome  the  peculiar  resistance  offered  by  the  surface 
of  the  water.  What  causes  that  resistance? 

SURFACE-TENSION.  The  force  responsible  for  the  floating  of  the 
needle  is  called  'surface-tension.'  It  is  a  manifestation  of  cohesion, 

-SURFACE  / 


FIG.  2 

which  is  the  attraction  that  binds  molecules  of  like  kind  to  each  other. 
Each  molecule  within  the  interior  of  the  liquid  is  imagined  as.  sur- 
rounded by  molecules  like  itself  to  which  it  is  attracted  and  which  it 
attracts  equally  in  every  direction,  whereas  the  molecules  at  the  free 
surface  of  the  liquid  are  attracted  only  by  those  internal  to  them- 
selves, the  result  being  to  constrict  the  free  surface  of  the  liquid.  In 
consequence,  the  surface  acts  as  if  it  were  a  stretched  membrane  or  an 
elastic  film.  These  molecular  conditions  may  be  represented  graph- 
ically. See  Pig.  2.  The  attractive  forces  acting  on  a  molecule  (A) 
in  the  body  of  the  liquid  may  be  represented  by  four  resultant  axial 
components,  which  are  equal,  so  that  the  molecule  is  perfectly  free  to 
move,  except  for  viscous  resistance.  At  the  surface  itself  the  upward 


21  tried  five  large  greased  needles,  all  of  which  floated;  then  I  tried  the 
same  needles  after  they  had  been  washed  in  the  soda  solution  and  wiped 
dry  on  a  clean  cloth.  One  time  all  five  sank;  the  other  time  four  sank. 


36  FLOTATION 

component  disappears  and  the  pull  downward  on  the  molecule  (B)  is 
uncompensated,  any  extension  of  the  surface  being  opposed  by  a  force 
the  horizonal  component  of  which  is  'surface-tension'. 

This  can  be  illustrated  in  another  way.  Each  particle  of  water  is 
attracted  by  all  the  particles  that  lie  within  its  range,  which  is  defi- 
nitely small,  about  0.00000015  cm. ;  therefore  the  scope  of  molecular 
attraction  may  be  considered  as  a  sphere  of  influence.  Thus  A  in 
Fig.  3  is  attracted,  and  attracts,  within  a  definite  sphere,  while  B, 


FIG.  3 

which  is  close  to  the  surface,  is  more  attracted  inward  than  outward, 
since  a  part  of  its  sphere  of  attraction  lies  outside  the  water. 

Such  a  hypothesis  is  largely  an  abstraction ;  a  concrete  idea  of  the 
nature  of  surface-tension  can  be  obtained  by  noting  some  of  its  various 
manifestations. 

1.  The  drawing,  or  'soaking  up',  of  water  by  a  sponge. 

2.  The  penetration  of  wood  by  varnish. 

3.  The  rising  of  oil  in  a  lamp:wick. 

4.  The  clinging  of  ink  to  a  pen. 

5.  The  running  of  the  ink  from  the  pen  to  the  paper. 

6.  The  absorption  of  the  excess  of  ink  by  blotting-paper. 

7.  The  cohesion  between  two  plates  that  have  been  wetted. 

8.  Dip  a  camel's  hair  brush  in  water,  remove  it  from  the  water, 
and  observe  how  the  hairs  cling  together.     Immerse  the  brush  in  the 
water  and  note  how  the  hairs  separate. 

9.  Watch  the  water-spiders  running  over  a  pool,  like  boys  skating 
on  thin  ice.    H.  H.  Dixon  actually  measured  the  pressure  exerted  by 
the  spider's  feet  on  the  water.     He  photographed  the  shadow  of  the 
dimple,  then  mounted  one  of  the  spider's  feet  on  a  delicate  balance, 
and  made  it  press  on  the  water  until  it  made  a  dimple  of  the  same 
depth  as  that  previously  recorded. 

10.  Pour  colored  water  in  a  thin  layer  over  the  bottom  of  a  white 


PRINCIPLES    OF    FLOTATION  37 

dish ;  then  touch  a  part  of  its  surface  with  a  glass  rod  that  has  been 
dipped  in  alcohol.  The  colored  water  shrinks  from  the  part  touched, 
leaving  an  irregular  patch  of  white  bottom  dry.  This  is  due  to  the 
tension  of  the  pure  water  being  greater  than  that  of  the  alcoholized 
water,  so  that  the  liquid  is  pulled  away  from  the  place  where  the 
tension  is  weak  to  the  place  where  it  is  strong.3  The  lively  movements 
of  the  particles  of  dye  in  the  water  indicate  the  conflict  between  the 
forces  of  diffusion  and  surface-tension. 

11.  The  formation  of  a  drop  at  the  end  of  a  tube  or  from  the  small 
mouth  of  a  bottle  is  another  example  of  surface-tension.     Note  how 
the  drop  grows  slowly  until  it  has  attained  a  definite  size,  and  then 
breaks  away  suddenly.     The  size  of  the  drop  is  always  the  same  for 
the  same  liquid  coming  through  the  same  orifice.     It  hangs  as  if  sus- 
pended in   an  elastic  bag  that  ruptures  when   the  weight  becomes 
excessive.     The  contractile  character  of  surface-tension  is  manifested 
in  the  formation  of  the  drop,  the  force  tending  to  draw  the  fragment 
of  liquid  into  the  most  compact  form,  that  presenting  the  least  surface 
in  relation  to  volume,  namely,  a  sphere. 

Similarly,  if  we  admit  air  through  a  glass  tube  of  given  size  into 
various  liquids,  we  shall  obtain  the  biggest  bubble  in  the  liquid  with 
the  highest  surface-tension.  If  various  liquids  in  succession  are 
allowed  to  run  out  of  an  opening  of  given  size,  the  largest  drop  will  be 
that  of  the  liquid  having  the  highest  surface-tension. 

12.  When  an  iron  ring  is  dipped  into  a  solution  of  soap  and  then 
taken  out,  it  will  be  seen  that  a  film  of  solution  stretches  across  the 
ring,  covering  the  whole  interior  circular  space.     If  a  small  loop  of 
cotton,  previously  moistened  in  the  soapy  solution,  is  placed  on  the 
film  stretched  across  the  circle  of  the  ring,  this  loop  can  be  made  to 
assume,  and  to  retain,  any  form,  such  as  is  shown  at  A  in  Fig.  4.    If, 
however,  this  film  within  the  loop  is  broken,  the  loop  immediately 
assumes  the  form  of  a  perfect  circle,  as  shown  at  B ;  and  if  it  is  now 
deformed  in  any  way,  it  springs  back  at  once  to  a  circle  as  soon  as  it 
is  released.     Evidently  the  surface  of  the  solution  assumes  the  shape 
covering  the  smallest  area.     The  surface-tension  of  the  liquid  acts 
equally  on  both  sides  of  the  cotton  so  long  as  it  is  wholly  immersed,  but 
when  the  film  of  liquid  inside  the  loop  is  broken,  the  tension  acts  on 
one  side  only — on  the  open  side,  where  it  is  in  contact  with  air — and 
hence  draws  the  loop  into  a  circle,  which  involves  the  minimum  of 
extension. 


-This  simple  experiment  is  a  fascinating  exhibition  of  surface-tension  and 
it  should  be  made  by  every  student  of  flotation. 


38 


FLOTATION 


FIG.  4 


13.  The  contractile  force  of  surface-tension  is  shown  in  a  simple 
way  by  blowing  a  soap-bubble  on  the  large  end  of  a  pipe  and  then 
holding  the  other  end  of  the  pipe  to  a  candle,  whereupon  the  air 
escaping  from  the  shrinking  bag  of  the  bubble  will  extinguish  the 
flame,  as  in  Fig.  5.4 


FIG.  5 


14.  When  water  is  sprinkled  on  a  dusty  floor,  the  dust  prevents 
the  wetting  of  the  floor  by  obstructing  the  coalescence  of  the  drops, 
that  is,  the  spreading  of  the  water  over  the  floor.  The  water  draws 
itself  into  rolling  spherules  that  become  armored  by  particles  of  dust. 
They  are  nearly  round,  the  larger  ones  showing  a  flattening,  because 


4C.  V.  Boys  in  'Soap  Bubbles'. 


PRINCIPLES    OF    FLOTATION  39 

* 

the  gravitational  stress  overcomes  the  contractibility  or  sphericity  of 
the  film.  This  flattening  is  shown  by  a  drop  of  mercury  on  glass  or  by 
the  beads  of  gold  on  an  assayer's  cupel. 

15.  The  globular  form  assumed  by  water  when  spilled  on  a  hot 
stove  is  another  manifestation  of  these  forces.    The  water  is  protected 
from  the  hot  iron  by  a  film  of  steam,  which,  as  it  is  formed,  decreases 
the  size  of  the  globule  until  it  disappears.    If  the  iron  is  not  sufficiently 
hot,  it  becomes  cooler  and  therefore  wetted,  by  spreading  of  the  water, 
which  is  instantly  converted  into  steam. 

16.  Some  of  the  physics  of  flotation  can  be  illustrated  at  the 
dinner-table. 

A.  Fill  a  glass  a  little  over-full  of  water  and  note  the  convex 
surface,  indicating  the  play  of  a  force  that  prevents  the  liquid  from 
spilling.    It  is  a  contractile  force. 

B.  Fill  a  wine-glass  half -full  with  port  and  observe  how  the  wine 
climbs  up  the  side  of  the  glass,  forming  a  meniscus  around  the  circum- 
ference of  the  surface.    This  liquid  consists  of  alcohol  and  water,  both 
of  which  evaporate,  the  alcohol  faster  than  the  water,  so  that  the 
surficial  layer  becomes  watery.    In  the  middle  of  the  glass  the  surficial 
layer  recovers  its  strength  by  diffusion  from  below,  but  the  film  adher- 
ing to  the  glass,  being  more  exposed  to  the  air,  loses  its  alcohol  by 
evaporation  more  quickly  and  therefore   acquires  a  surface-tension 
higher  than  that  of  the  undiluted  wine.    It  creeps  up  the  side  of  the 
glass  dragging  the  strong  wine  after  it,  and  this  continues  until  the 
quantity  of  fluid  pulled  upward  collects  into  drops — called  the  'tears 
of  wine' — that  run  back  into  the  glass. 

C.  Fill  a  a  glass  two-thirds  full  from  a  'siphon'  containing  water 
that  is  effervescent  because  it  contains  gas  in  solution.    Take  three  or 
four  small  grapes,  preferably  of  the  Californian  seedless  variety.    The 
grapes  will  sink  to  the  bottom  of  the  glass,  but  soon  they  become  restless 
and  rise  to  the  surface,  one  after  the  other.    They  do  not  remain  there 
long ;  first   one  and  then  the  other  sinks.    They  will  continue  the  per- 
formance for  half  an  hour,  bobbing  up  and  down;  their  activities 
slowly  diminish,  and  eventually  they  are  left  inert  at  the  bottom  of 
the  glass.     What  happens  is  simple  enough.     The  siphon  has  come 
from  the  refrigerator;  the  warmth  of  the  room  and  the  lowering  of 
pressure  release  the  carbonic-acid  gas,  which,  in  the  form  of  minute 
bubbles,  attaches  itself  to  the  grapes,  buoying  them  to  the  surface  as 
mineral  particles  are  raised  to  the  surface  of  a  pulp  in  the  Potter 
process.    There  the  bubbles  burst,  causing  the  grapes  to  fall  back.    If 
"a  couple  of  grapes  collide,  the  bubbles  become  detached,  dropping 


40 


FLOTATION 


their  freight,  and  themselves  rising  to  the  surface.  At  first  the  grapes 
rise  rapidly  and  rebound  from  the  surface  of  the  water  as  if  it  were 
an  elastic  membrane.  This  is  a  remarkable  effect  and  should  be  noted 
carefully.  After  the  evolution  of  gas  has  diminished  the  bubbles 
become  too  few  to  buoy  the  grapes,  and  the  performance  ends. 

Surface-tension  is  identified  with  'capillarity',  because  it  is  so 
marked  in  a  tube  the  bore  of  which  is  only  large  enough  to  admit  a 
capillus,  or  hair.  When  the  lower  end  of  a  wide  tube  is  held  in  water, 
the  water  inside  rises  to  about  the  same  level  as  that  outside  the  tube, 
in  accordance  with  the  law  of  hydrostatic  pressure;  but  when  the 
lower  end  of  a  glass  tube  of  small  bore,  say,  1  mm.,  open  at  both  ends, 
is  inserted  into  water,  the  water  rises  within  the  tube  and  stands  at  a 
level  higher  than  the  water  outside.  If,  again,  the  tube  be  held  ver- 
tically with  its  lower  end  immersed  in  mercury,  the  liquid  metal  inside 
the  tube  sinks  to  a  level  below  that  of  the  mercury  outside.  See  Fig. 
6.  This  is  explained  by  saying  that  the  molecular  attraction  of  water 


Fro.  6 


GLASS   TUBE  IN   WATER 


GLASS   TUBE   IX   MERCURY 


to  glass  is  greater  than  that  of  water  to  water ;  whereas  the  attraction 
of  mercury  to  glass  is  less  than  that  of  mercury  to  mercury.  The  forces 
of  cohesion  in  a  substance  and  of  adhesion  between  various  substances 
have  been  measured.  Quincke  and  others  have  ascertained  by  experi- 
ment that  the  effect  is  sensible  within  a  range  of  one  thousandth  and 
one  twenty-thousandth  of  a  millimetre.  Such  is  the  scope  of  molecular 
attraction.  The  liquid  rises  in  a  capillary  tube  until  the  weight  of  the 
vertical  column  between  the  free  surface  and  the  level  of  the  liquid  in 
the  tube  balances  the  resultant  of  the  surface-tension. 

The  surface-tension  of  liquids  can  be  modified.  It  is  decreased  by 
a  rise  of  temperature.  For  example,  place  two  matches  an  inch  apart 
on  the  surface  of  pure  water  in  a  bowl  and  then  touch  the  water  be- 
tween them  with  a  hot  wire.  They  draw  apart  promptly,  because  the 
surface-tension  of  the  water  between  them  has  been  lowered  relatively 


PRINCIPLES   OF    FLOTATION  41 

to  that  of  the  rest  of  the  liquid  in  the  bowl,  so  that  the  pull  of  the  water- 
surface  under  normal  tension  is  stronger  than  that  of  the  surface  of 
the  warm  water  between  the  matches. 

The  addition  of  an  impurity  or  contaminant  will  lower  the  surface- 
tension  of  water.  We  have  seen  how  this  effect  is  caused  both  by 
alcohol  and  soap.  Distilled  water  has  a  maximum  surface-tension, 
which  is  lowered  by  almost  any  substance  that  is  soluble  or  miscible 
in  it.  The  soluble  substance,  or  solute,  modifies  the  tension  directly, 
whereas  the  minutely  divisible  substance,  forming  an  emulsion,  creates 
a  great  number  of  interfaces,  or  surfaces  of  contact,  each  having  a 
lower  tension.  The  particular  contaminant,  or  modifying  agent,  asso- 
ciated with  the  early  history  of  flotation  was  oil,  which  is  partly  soluble 
and  readily  dispersible.  The  oil  generally  used  at  first  was  a  heavy 
oil,  like  oleic  acid.5  By  the  addition  of  sufficient  oil  the  surface-tension 
of  water  is  lowered  from  73  to  14  dynes  per  linear  centimetre.  The 
following  experiment  illustrates  this  fact.  If  a  wooden  match  be  laid 
on  the  surface  of  tap-water  in  a  pan,  so  that  it  remains  at  rest,  and  if 
then  a  drop  of  olive-oil  be  placed  on  the  surface  of  the  water  near  the 
match,  the  match  will  draw  away  smartly,  because  the  oil  has  reduced 
the  tension  of  part  of  the  water-surface  and  caused  the  uncontaminated 
water  to  pull  away.  This  modification  of  the  surface-tension  of  water 
by  a  contaminant  is  one  of  the  fundamental  factors  in  flotation,  as  we 
shall  see. 

Let  us  now  go  back  to  the  floating  needle.  If  it  is  greased,  does 
the  grease  lower  the  surface-tension  of  the  water?  That  can  be  ascer- 
tained by  a  pretty  experiment.  If  camphor  is  whittled  with  a  knife 
above  a  bowl  of  water  the  shavings,  dropping  on  the  water,  will  dance 
on  the  surface  in  a  life-like  manner  suggesting  insects  in  a  fit.  This 
phenomenon,  as  shown  by  Marangoni,  is  due  to  the  dissolving  of  the 
camphor — a  crystalline  vegetal  distillate — preferably  at  the  pointed 
end,  where  the  largest  area  per  unit  of  volume  is  presented  for  solution. 
The  dissolving  of  the  camphor  lowers  the  surface-tension  of  the  water 
in  contact  and  thereby  causes  the  uncontaminated  water,  with  its 
stronger  tension,  to  pull  away  from  the  spot  affected  by  the  camphor — 
as  in  the  colored  water  and  alcohol  experiment,  No.  10.  This  causes 
the  chips  of  camphor  to  turn  and  move  spasmodically.  In  order  to 
incite  such  activity  the  surface-tension  of  the  water  must  be  greater 
than  that  of  the  camphor  solution.  As  soon  as  enough  camphor  has 
dissolved  to  modify  the  whole  surface  of  the  water  in  the  bowl  or  cup, 


&No  wonder  the  judges  were  puzzled  by  the  technical  terms  used  in  flota- 
tion lawsuits.  'Oleic  acid'  is  called  an  oil,  whereas  'oil  of  vitriol'  is  an  acid. 


42  FLOTATION 

the  chips  become  inert.  Likewise  if  the  surface-tension  be  lowered 
by  the  addition  of  grease  the  camphor  remains  quiet.  For  example, 
if,  while  the  chips  of  camphor  are  lively,  the  water  be  touched  by  a 
greasy  finger — all  fingers  are  slightly  greasy — the  camphor  is  quieted 
immediately.  No  ordinary  'clean'  cooking-utensil  is  sufficiently  free 
from  grease  to  allow  an  exhibition  of  the  camphor  dance. 

Here  we  have  a  simple  means  of  detecting  the  presence  of  grease  or 
oil  in  the  water  upon  which  the  needle  is  floating.  I  introduced  some 
camphor  chips  into  the  water  on  which  the  ungreased  needle  was  float- 
ing and  they  became  lively.  Then  I  repeated  the  experiment  with  a 
needle  that  was  slightly  greased,  by  rubbing  it  with  the  fingers  that 
had  touched  my  hair,  and  the  camphor  appeared  unaffected  thereby; 
it  was  lively.  Finally,  I  smeared  the  needle  with  olive-oil;  an  irides- 
cence on  the  surface  of  the  water  indicated  diffusion  of  the  oil.  This 
time  the  chips  of  camphor  fell  dead  as  a  door-nail  and  remained  wholly 
inert  on  the  water.  Apparently,  therefore,  the  needle  will  hold  to  itself 
a  limited  proportion  of  oil,  which  adheres  so  selectively  as  not  to  con- 
taminate the  water;  but  an  excess  of  oil,  more  than  the  needle  can 
hold,  will  be  set  free  at  once  to  modify  the  water  and  lower  its  surface- 
tension. 

This  is  a  classic  experiment,  as  I  ascertained  afterward.  Raleigh 
showed  that  the  decrease  of  surface-tension  begins  as  soon  as  the 
quantity  of  oil  is  about  half  that  required  to  stop  the  camphor  move- 
ments, and  he  suggested  that  this  stage  may  synchronize  with  a  com- 
plete coating  of  the  surface  with  a  single  layer  of  molecules.0 

A  reference  has  been  made  already  to  the  measuring  of  surface- 
tension.  It  can  be  done  in  several  ways.  For  example,  a  framework, 
such  as  is  shown  in  Fig.  7,  is  constructed7  out  of  a  transverse  bar  AB 
and  two  grooved  slips  CD  and  EF,  so  as  to  allow  a  piece  of  wire  GHIJ 
to  slip  freely  up  and  down.  The  wire  HI  is  pushed  against  AB  and 
some  of  the  liquid  is  applied  between  them.  The  little  pan  X  is  loaded 
with  sand  so  that  the  wire  HI  is  pulled  gently  from  AB.  The  mini- 
mum force  required  to  do  this  is  mg,  the  weight  of  M  grammes.  This 
weight  suspended  on  the  film  of  liquid  between  AB  and  HI  equals  the 
tension  of  the  film  on  the  wire.  If  the  film  stretches  until  the  wire  HI 
is  at  p,  then  the  film  has  an  area  C%,  CP.  The  total  weight  mg  is 
distributed  over  the  breadth  CE,  whence  if  T  represents  the  surficial 
tension  across  the  unit  of  length  CE,  then 

>r  T=~CE 


eThe  Encyclopaedia  Britannica.     llth  Edition.     Page  267. 

7  Alfred  Danniell.    'A  Text  Book  of  the  Principles  of  Physics'. 


PRINCIPLES    OF    FLOTATION 


43 


H 


X 

FIG.  7 


r 
i 


Another  simple  way  of  measuring  surface-tension  is  to  make  a  wire- 
frame of  which  one  side  is  movable;  thus  (Fig.  8)  let  ABC  represent 
a  bent  wire  and  DE  a  straight  piece.  If  a  film  of  liquid  is  spread 


FIG.  8 


44  FLOTATION 

over  the  space  DBE  then  the  surface-tension  acting  011  DE  will  support 
not  only  the  weight  of  the  wire  DE  but  also  a  small  weight  X.  If  W 
be  the  mass  of  the  cross-wire  DE  and  its  attached  weight,  then  the 
surface-tension  of  the  film  supports  W  and  exerts  a  force  Wg.  The 
surface-tension  acts  all  along  that  part  (1)  of  the  wire  DE  that  lies  in 
contact  with  the  film,  and  it  acts  at  right  angles  to  DE.  Since  the  film 
has  two  surfaces,  if  the  force  exerted  on  a  unit  length  of  DE  and  on 
one  side  of  the  film  be  T,  then  the  upward  force  on  DE  due  to  surface- 

Wo 
tension  is  2TI.     Hence8  if  there  is  equilibrium  2Tl=  Wg,  or  T  ^—^ 

This  method  was  suggested  by  Clerk  Maxwell.  An  ingenious 
mechanical  model  for  illustrating  the  definition  of  surface-tension  has 
been  devised  by  Frank  B.  Kenrick,  of  the  University  of  Toronto.  He 
gives  the  definition  as  "the  maximum  quantity  of  work  that  can  be 
gained  when  a  surface  is  decreased  in  area  by  one  square  centimetre", 
and  describes  his  device  as  follows:  "A  projection  cell  40  mm.  by 
10  mm.  and  60  mm.  high,  the  upper  edges  of  which  have  been  coated 
with  a  film  of  paraffine-wax,  is  filled  almost  to  overflowing  with  water. 
On  the  surface  is  floated  a  thin  shaving  of  cork  30  mm.  by  5  mm.  by  1 
mm.,  to  which  is  attached  a  fine  cotton  thread  about  40  mm.  long  ter- 
minating in  a  little  glass  hook.  The  thread  passes  over  a  small  pulley 
made  from  a  pill-box  and  a  pin  resting  in  a  double  Y-shaped  glass 
bearing.  Three  weights  of  glass  or  bent  wire  weighing  about  0.1 
gramme,  0.07  gm.,  and  0.04  gm.  may  be  hung  on  the  hook.  The  middle 
weight  approximately  balances  the  surface-tension,  while  the  lighter 
one  on  being  pulled  down  with  a  pair  of  tweezers  is  lifted  again  by  the 
surface-tension.  A  fall  of  1  c.c.  produces  one  square  centimetre  of 
surface,  namely,  0.5  cm2  on  the  forward  under  side  of  the  cork  that  is 
wet  with  water  and  0.5  cm2  on  the  upper  surface  of  the  liquid  in  the 
cell."9  For  the  accompanying  sketch  (Fig.  9)  I  am  indebted  to  Pro- 
fessor Kenrick,  who  sent  it  to  me  on  request.  The  waxing  of  the  upper 
edge  of  the  glass  cell  allows  the  water,  which  does  not  wet  paraffine,  to 
rise  slightly  higher  than  the  level  of  the  glass  without  overflowing. 

By  such  experiments  the  force  of  surface-tension  between  water  and 
air  has  been  determined  to  be  3.14  grains  per  linear  inch  or  72.62 
dynes  per  centimetre  at  20° C.10  Many  disturbing  factors  enter  into 


«W.  Watson.    'A  Text-book  of  Physics',  p.  182. 

»Jour.  of  Phys.  Chem.,  Vol.  XVI,  page  513. 

i  ("Theodore  W.  Richards  and  Leslie  B.  Coombs.  'The  Surface-Tension  of 
Water,  Alcohols,  etc.'  Jour.  Amer.  Chem.  Soc.,  July  1915.  One  dyne  is  equal 
to  1.02  milligrams. 


PRINCIPLES   OF    FLOTATION 


45 


the  measurement  of  this  force,  so  that  divers  figures,  ranging  from 
70.6  to  81  have  been  announced  at  various  times.11 

This  force  may  seem  small,  yet  the  actual  tensile  strength  per  unit- 
area  of  cross-section  of  the  film  is  about  one-fourth  that  of  the  iron  or 
mild  steel  used  in  the  shells  of  steam-boilers,  although  its  density  is  not 
much  more  than  one-eighth  as  great  as  that  of  the  iron.12 

The  surface-tension  of  a  liquid  must  be  stated  with  reference  to 
the  fluid — gas  or  liquid — in  contact,  for  it  is  modified  by  the  nature  of 
the  substance  on  either  side  of  the  interface.  An  interfacial  tension 
exists  at  any  surface  separating  two  substances  and  it  has  a  particular 


I ,?- 


Is 


FIG.  9 


value  for  each  pair  of  substances.  For  example,  the  tension  separating 
mercury  from  water  is  418  dynes  per  centimetre  whereas  that  sep- 
arating olive-oil  from  air  is  only  36.9  dynes.  A  drop  of  water  will  not 
spread  over  the  surface  of  mercury  but  oil  will  spread  over  water. 
The  balance  of  forces  is  different  in  the  two  cases.  When  a  globule  of 
oil  is  placed  on  water,  the  tension  of  the  water-air  surface  exerts  a  pull 
of  73  dynes  as  against  the  joint  pull  (37  plus  14)  of  the  air-oil  and 


nT.  J.  Hoover  in  his  valuable  book  'Concentrating  Ores  by  Flotation' 
quotes  from  Clerk  Maxwell's*  article  on  'Capillarity'  in  the  Encyclopaedia 
Britannica  and  gives  the  figures  as  81,  but  he  makes  the  mistake  of  saying 
that  it  is  81  dynes  "per  square  centimetre."  It  is  a  tension,  not  a  pressure. 

i2M.  M.  Garver.    Jour.  Phys.  Chem.,  Vol.  XVI,  page  243. 


46  FLOTATION 

oil-water  surfaces.  Thus  14  -f  37  <  73.  (Fig.  10).  The  oil  spreads. 
If  soap,  in  the  form  of  \%  sodium  oleate,  be  added  to  the  water  its 
surface-tension  will  be  lowered  to  26  and  the  oil-water  tension  will  also 
be  decreased,  how  much  I  do  not  know,  but  certainly  decreased,  say, 
to  12;  therefore  37  +  12  >  26,  and  the  oil  will  not  spread  over  the 
water.  On  the  other  hand,  the  tension  of  the  mercury-air  surface  has 
been  given  as  436  dynes  and  that  of  the  mercury-water  surface  as  418. 

37  *.  37^ 

AIP         ^^^  ^73  A I  ft         ^-rrr^  ^6 


WATfff       ^~~~/^  SOAPY 

FIG.  10 

If  this  be  so,  then  a  drop  of  water  will  not  spread,  because  418  -f-  73 
>  456.  But  Quincke  showed  long  ago  that  pure  water  will  spread  on 
pure  mercury,  although  the  presence  of  an  impurity,  such  as  a  slight 
greasiness,  on  the  surface  of  the  mercury  will  prevent  spreading. 
According  to  later  determinations  of  the  interfacial  tensions,  by 
Freundlich,  that  of  mercury-air  is  445  dynes  and  that  of  mercury- 
water  370,  so  that  73  +  370  <  445,  and  the  pure  water  ought  to  spread 
on  the  pure  mercury,  as  Quincke  stated.  If  the  water  be  contaminated, 
so  as  to  lower  its  surface-tension,  it  will  spread  readily  even  on  ordi- 
nary mercury,  which  is  not  chemically  pure  and  on  which  pure  water 
will  not  spread. 

WETTING.  A  steel  needle  floats  on  water,  but  a  glass  rod  of  the 
same  size  sinks  immediately ;  yet  the  specific  gravity  of  steel  is  to  that 
of  glass  as  8  to  2.75.  The  surface  of  the  water  resists  rupture  by  the 
steel  but  it  is  readily  broken  by  the  glass;  in  other  words,  the  glass  is 
readily  'wetted,'  while  the  steel  is  not.  Again,  if  the  glass  rod  be 
greased  it  will  float ;  it  ceases  to  be  easily  wetted.  Here  we  face  one 
of  the  underlying  phenomena  of  flotation.  The  understanding  of  what 
constitutes  'wetting'  is  essential  to  the  subject. 

If  a  drop  of  pure  water  be  placed  on  a  clean  piece  of  glass,  it  will 
flatten  itself  out  so  as  to  increase  the  space  it  first  touched.  If  a  similar 
drop  of  water  be  placed  on  a  cabbage-leaf,  it  will  not  spread,  but  will 
retain  its  spherical  form.  We  say  that  water  'wets'  a  glassy  surface 
and  does  not  'wet'  a  waxy  vegetal  surface.  A  drop  of  mercury  spreads 
eagerly  over  gold,  but  does  not  spread  on  glass ;  mercury  wets  gold  but 
not  glass.  The  statement  is  not  absolute ;  it  is  a  question  of  degree. 

If  I  press  the  surface  of  water  with  a  piece  of  glass  the  water  rises 
to  meet  the  glass,  forming  a  mound,  whereas  if  I  make  the  same  test 


PRINCIPLES   OF    FLOTATION 


47 


with  a  piece  of  steel  the  water  shrinks  away  from  it,  forming  a  depres- 
sion. The  tendency  is  for  the  water  to  lap  the  glass  but  to  avoid  the 
steel;  the  one  substance  is  easily  'wetted/  the  other  not.  The  glass 
and  the  steel  typify  the  gangue  and  the  sulphide  respectively  in  an  ore 
treated  by  flotation.  If  we  look  carefully  at  the  steel  and  glass,  at  the 
instant  of  touching  the  water,  we  see  the  conditions  sketched  in  Fig.  11. 

FIG.  11 

Note  how  ink  from  a  pen  will  not  run  on  paper  that  is  at  all  greasy. 
The  paper  refuses  to  be  wetted  where  it  is  greased.  That  is  why  new 
pens  are  refractory ;  the  steel  has  been  greased  to  prevent  rusting,  like 
the  needles.  I  used  to  burn  the  point  of  a  new  pen  by  aid  of  a  match  in 
order  to  cause  it  to  deliver  the  ink  to  the  paper  comfortably.  That 
burned  the  grease,  but  spoiled  the  temper  of  the  pen-point. 

The  free  surface  of  a  liquid  is  horizontal,  but  at  the  contact  with  a 


FIG.  12 


FIG.  13 


solid  the  surface  is  curved,  the  direction  and  amount  of  curvature 
varying  as  between  different  liquids  and  solids.  The  water  curves 
upward  against  glass,  whereas  it  curves  downward  against  steel;  it 
tends  to  drown  the  one,  but  to  float  the  other  until  gravity  overmasters 
surface-tension.  The  way  in  which  a  liquid  impinges  on  a  solid  is 
called  the  'angle  of  contact.'  For  example,  in  Fig.  12  water  is  shown 
in  contact  with  glass.  Consider  the  conditions  at  the  point  O.  The 


48  FLOTATION 

gravitational  pull  on  a  minute  quantity  of  the  water  is  negligible  in 
comparison  with  its  own  cohesive  force ;  so  we  can  disregard  the  effect 
of  gravity.  The  force  of  adhesion  exerted  by  the  surface  of  the  glass 
is  reperesented  by  O  A,  the  force  of  cohesion  in  the  water  is  represented 
by  O  B,  and  the  resultant  of  these  two  forces  is  O  C.  If  the  adhesive 
force  of  the  liquid  to  the  solid  exceeds  the  cohesive  force  of  the  liquid, 
the  resultant  will  lie  to  the  left  of  the  vertical,  E  D,  that  is,  within  the 
solid;  and  since  the  surface  of  a  liquid  assumes  a  position  at  right 
angles  to  this  resultant  force,  the  water  rises  on  the  face  of  the  glass. 
If,  on  the  other  hand,  as  in  Fig.  13,  where  steel  is  shown  in  water,  the 
cohesion  of  the  liquid  is  greater  than  the  adhesion  of  the  liquid  to  the 
solid,  then  the  resultant  force  lies  to  the  right  of  the  vertical,  or  within 
the  liquid,  which  accordingly  is  depressed  at  the  face  of  the  solid. 

In  Fig.  12  and  13  the  contact-angle  is  DOB.  Since  the  surface  of 
the  liquid  always  assumes  a  position  at  right  angles  to  the  resultant 
force,  the  water  will  tend  to  rise  on  the  glass  and  to  sink  on  the  steel. 
This  angle  of  contact  between  a  liquid  surface  and  a  solid  is  usually 
the  same  for  the  same  pair  of  substances,  but  there  is  a  subtle  varia- 
tion, which  is  called  'hysteresis'  and  it  is  said  to  play  an  important 
part  in  flotation.  The  variation  is  connected  with  the  ability  of  a  solid 
to  condense  a  film  of  gas  upon  its  surface.  This  gas-condensing  power, 
or  adsorption,  can  be  modified,  by  acidulatiori,  for  example.  Sulman 
has  stated  that  "whereas  the  angular  hysteresis  of  silica  in  plain  water 
may  exceed  30°,  thus  indicating  that  substance  to  have  a  definite  power 
to  occlude  gas  and  to  float,  it  drops  from  4°  to  nil  in  water  acidulated 
with  sulphuric  acid.  Galena,  on  the  other  hand,  retains  its  full  meas- 
ure of  angular  variation,  or  is  but  slightly  affected. '  '13  This  effect  of 
the  surface-energy  of  solids  is  apparently  an  important  factor  in  flo- 
tation, and  it  is  a  pity  that  the  exigencies  of  patent  litigation  have 
prevented  Mr.  Sulman  from  contributing  more  to  the  technology  of 
the  subject. 

The  angle  of  contact  between  water  and  glass  is  so  acute  as  to  be 
more  nearly  zero  the  purer  the  water  and  the  cleaner  the  glass ;  between 
turpentine  and  glass  it  is  17°  ;  between  mercury  and  glass  it  is  148°. 
In  a  general  way,  subject  to  the  variation  already  noted,  the  size  of 
the  contact-angle  measures  the  capacity  for  '  wetting. '  This  angle  can 
be  changed  by  modifying  the  surface-tension  of  the  water  by  means  of 
a  contaminant,  such  as  oil,  or  the  angle  can  be  altered  by  modifying 
the  surface  of  the  solid,  also  by  oiling.  The  oiling  of  the  steel  needle 


i«H.    L.    Sulman.      Presidential    address.      Trans.    I.    M.    &    M.,   Vol.    XX. 
p.  XLVII. 


PRINCIPLES   OF    FLOTATION  49 

increased  the  angle  of  contact  with  the  water  so  that  it  did  not  impinge 
as  directly  on  the  needle,  and  it  did  the  same  to  the  glass  rod,  but  the 
effect  was  relatively  less  on  the  steel  than  on  the  glass  because  of  the 
higher  specific  gravity  of  the  former.  The  force  tending  to  prevent 
sinking  depends  upon  the  radius  of  the  needle,  its  density  relative  to 
that  of  the  water,  the  surface-tension  of  the  water,  and  the  cosine  of 
the  contact-angle.14  In  metallurgical  practice  the  pull  of  gravity  is 
decisive  in  so  far  as  it  limits  the  size  of  particle  that  can  be  floated  in 
water.  If  our  needle  is  too  large,  it  sinks,  no  matter  how  favorable  the 
other  conditions  may  be.  So  the  flotation  of  a  particle  of  mineral  is 
conditioned  on  the  size  to  which  it  has  been  reduced  by  crushing  in 
the  mill.  The  oiling  of  the  needle  increased  the  upward  component  of 
the  surface-tension  by  enlarging  the  angle  of  contact,  but  the  use  of  an 
excess  of  oil,  that  is,  more  than  the  needle  could  hold  of  itself,  served 
to  lower  the  surface-tension  of  the  water  and  therefore  to  diminish  the 
resultant  force  operating  against  wetting  and  in  favor  of  flotation. 
Thus  the  oil  used  in  flotation  has  two  possible  functions,  and  they 
may  interfere  with  each  other. 

If  to  the  water  in  which  a  needle  is  floating  I  add  a  drop  of  pine- 
oil,  the  needle  sinks  at  once  because  the  lowering  of  the  surface-tension 
enables  the  water  to  wet  the  needle,  that  is,  to  diminish  the  angle  of 
contact  so  that  the  water  envelopes  the  steel.  Let  us  make  some  other 
simple  experiments.  Take  a  piece  of  chalcocite  that  presents  a  smooth 
surface.  A  drop  of  water  will  not  spread  over  it  as  it  will  on  glass ;  the 
globule  of  water  flattens  itself  on  the  glass  but  tends  to  retain  its 
spherical  form  on  the  chalcocite.  The  glass  may  typify  quartz  or  some 
other  gangue-mineral.  A  drop  of  flotation-oil,  such  as  coal-tar  creo- 
sote, flattens  on  the  chalcocite,  whereas  water  maintains  its  sphericity. 
Coal-tar  spreads  less  on  glass  than  on  water,  but  water  spreads  more 
on  glass  than  on  chalcolite.  Thus  water  wets  mineral  less  easily  than 
gangue,  whereas  oil  coats  mineral  more  readily  than  gangue.  So  we 
say  that  gangue  has  a  greater  affinity  for  water  than  mineral,  which, 
on  the  contrary,  has  a  greater  affinity  for  oil. 

Water  drips  off  oiled  copper  more  quickly  than  off  the  unoiled; 
there  is  more  adhesion  between  the  water  and  the  unoiled  metal;  the 
oil  prevents  wetting  by  the  water.  The  effect  of  the  density  of  the 
surrounding  medium  is  shown  by  placing  a  piece  of  glass  under  water, 
dropping  a  globule  of  coal-tar  upon  the  glass,  and  then  raising  it  out 
of  the  water.  The  globule  of  oil  spreads  when  lifted  out  of  the  denser 


!•» Joel    H.    Hildebrand.      'Principles   Underlying  Flotation.'     M.   &   S.   P.. 
July  29,  1916. 


50  FLOTATION 

medium  and  shrinks  when  returned  to  the  water,  although  not  quite 
to  its  first  shape,  on  account  of  the  adhesive  surface.  The  oil  on  the 
galena  replaces  the  water  on  its  surface,  but  the  oil  on  the  quartz  is 
unable  to  prevent  the  water  from  pushing  itself  underneath  and  over 
the  surface  of  the  quartz.  Thus  we  have  ' '  an  instance  of  the  selective 
action  of  oil  on  a  metallic  sulphide  in  the  presence  of  water,  and  the 
selective  action  of  water  on  a  gangue-mineral  in  the  presence  of  oil."15 
On  this  phenomenon  largely  depends  the  process  for  separating  valu- 
able mineral  from  worthless  gangue  by  flotation. 

If  a  piece  of  galena  and  a  piece  of  quartz  are  placed  under  water 
on  the  bottom  of  a  beaker  and  if  a  few  drops  of  oil,  such  as  wood- 
creosote,  are  dropped  upon  the  water,  they  will  descend  through  the 
water  owing  "to  their  momentum  and  the  releasing  of  the  surface- 
tension  of  the  water"16  until  one  may  fall  on  the  galena,  on  which  the 
oil  will  spread,  while  another  falls  on  the  quartz,  on  which  it  tends  to 
draw  into  globular  form,  instead  of  spreading.  Flotation  is  essentially 
a  selective  process.  If  I  throw  powdered  ore  on  water,  the  particles 
of  gangue  sink  and  the  particles  of  mineral  float,  in  accord  with  our 
expectation,  based  on  the  foregoing  experiments  and  the  deductions 
therefrom,  but  some  of  the  small  particles  of  gangue  will  float  and 
some  of  the  larger  particles  of  mineral  will  sink,  because  the  play  of 
forces  is  so  complex  that  any  single  one  of  them  is  not  uniformly  de- 
cisive. Flotation  is  preferential,  not  absolute. 

BUBBLES.  We  saw  how  the  floating  of  the  needle  was  aided  by 
bubbles  of  air  attached  to  it.  That  suggests,  but  does  not  explain,  the 
latest  and  most  successful  phase  of  flotation.  To  understand  it  we 
must  go  back  to  the  small  boy's  soap-bubble.  The  man  that  under- 
stands the  physics  of  a  soap-bubble  has  mastered  the  chief  mystery  of 
flotation.  The  boy,  who,  as  pictured  by  Milais,  watches  the  birth, 
ascent,  and  disappearance  of  the  iridescent  sphere  of  his  own  making, 
is  the  type  of  our  modern  metallurgist,  who  makes  the  multitudinous 
bubbles  constituting  a  froth  and  then  wonders  to  what  natural  laws 
his  filmy  product  owes  its  existence. 

To  put  it  briefly,  the  boy,  having  dissolved  soap  in  water,  holds  a 
little  of  the  liquid  in  the  bowl  of  his  clay  pipe  while  he  blows  through 
the  stem.  The  soapy  water  forms  a  film  that  is  distended  by  the  boy's 
warm  breath  into  a  lovely  sphere,  which  is  lighter  than  the  surround- 
ing air,  and  therefore  rises,  while  the  sunlight  falling  upon  it  under- 
goes refraction  into  the  colors  of  the  spectrum.  When  the  boy  blows 


ISA.  F.  Taggart,  as  witness  in  the  recent  trial,  at  Butte. 
i«Taggart,  op.  cit. 


PRINCIPLES   OF    FLOTATION  51 

through  his  pipe  into  pure  water,  he  makes  bubbles  likewise,  but  they 
burst  instantly.  The  high  tension  shatters  them.  They  do  not  burst 
explosively  by  expansion  of  the  air  within  their  envelope,  but  by 
lateral  displacement  of  the  substance  composing  their  incompletely 
elastic  films.  To  prevent  such  immediate  collapse  it  is  necessary  to 
lessen  the  tension,  that  is,  to  diminish  the  contractile  force  at  work  in 
the  watery  substance  constituting  the  exterior  of  the  bubble.  This  can 
be  done  by  introducing  an  impurity  or  contaminant.  Water  has  the 
highest  surface-tension  of  any  common  liquid,  so  that  the  addition  of 
almost  any  other  liquid — such  as  oil,  alcohol,  or  acid — will  lower  the 
tension.  The  boy  rubs  the  soap  between  his  wet  hands  and  dissolves  it 
in  the  water.  The  soluble  soaps  contain  an  alkaline  base,  such  as 
potash  or  soda,  combined  with  a  fatty  acid,  such  as  oleic  or  palmitic, 
extracted  from  tallow  or  oil.  The  boy  uses  oleate  of  soda,  a  compound 
of  soda  and  oleic  acid.  The  flotationist  uses  oleic  acid,  and  much  of 
the  early  work  was  done  with  this  thick  oil.  In  both  cases,  boy  or  man, 
playing  at  bubbles  or  working  at  metallurgy,  the  oil  serves  to  lower 
the  surface-tension  of  the  water  and  to  prolong  the  life  of  the  bubbles 
that  are  made  out  of  this  modified  water. 

Two  phases  of  the  subject  may  be  compared:  The  needle  that 
floats  on  tap-water  will  sink  in  distilled  water,  because  the  latter  lacks 
the  air-bubbles  that  assist  flotation.  Although  the  tap-water  has  a 
lower  surface-tension  on  account  of  its  slight  impurity,  that  effect  is 
less  decisive  than  the  aeration.  The  bubble  blown  in  pure  water  will 
break  almost  as  soon  as  it  comes  into  existence,  but  the  solution  of  a 
little  soap  in  the  water  will  enable  a  boy  to  blow  bubbles  that  sail  away 
beautifully.  The  lowering  of  the  surface-tension  by  the  contaminant 
lessens  the  tendency  of  the  bubbles  to  collapse.  We  have  seen,  in  the 
camphor  experiment,  how  the  oil  would  lower  the  surface-tension  not 
only  of  the  bubble-film  but  also  of  the  water  in  which  it  might  be  gen- 
erated ;  that  lowering  of  the  surface-tension  promotes  wetting,  which 
is  antithetic  to  floating.  If,  to  water  on  which  mineral  particles  are 
floating,  an  addition  of  alcohol  or  caustic  soda  be  made,  or  even  the 
vapor  of  alcohol  be  allowed  to  play  over  the  surface  of  the  water,  the 
mineral  particles  sink.  The  intense  local  contamination  of  the  water 
has  decreased  its  surface-tension  so  much  as  to  increase  the  relative 
effect  of  gravity.  Instant  wetting  ensues.  It  is  evident  therefore  that 
oil  can  be  used  effectively  in  flotation  in  two  ways:  Either  in  such 
large  quantity  as  to  raise  the  mineral  by  sheer  buoyancy  .or  in  such 
small  quantity  as  to  coat  the  particles  of  mineral,  in  preference  to  the 
gangue,  and  also  decrease  the  surface-tension  of  the  water  in  such  a 


52  FLOTATION 

way  as  to  promote  the  formation  of  a  stable  froth.  Luckily  the  in- 
creased wetting  power  of  the  water  due  to  the  solution  or  emulsincation 
of  the  oil  is  rendered  largely  ineffective  by  the  oiling  of  the  mineral 
particles  themselves,  on  the  surfaces  of  which  the  oil  displaces  the 
water  and  thus  prevents  wetting,  while  the  lack  of  adhesion  between 
oil  and  gangue  serves  differentially  to  aid  the  wetting  of  the  latter  by 
the  water. 

The  changing  colors  of  the  bubble  indicate  that  the  thickness  of  the 
film  is  not  constant ;  on  the  contrary,  it  may  vary  within  wide  limits 
without  noteworthy  variation  of  the  surface-tension.  That  makes  an 
important  difference  between  a  liquid  film  and  any  ordinary  elastic 
membrane.  "The  tension  in  a  liquid  film  is  independent  of  the 
stretching,  provided  that  it  is  not  so  great  as  to  reduce  the  thickness 
of  the  film  below  about  five  millionths  of  a  centimetre."17  This  result 
is  promoted  by  the  use  of  a  solute  that  will  be  strongly  adsorbed  at 
the  surface  of  the  solution.18  As  the  film  is  being  stretched,  the  new 
surface  formed  at  the  thinner  portion  will  contain  less  solute,  owing  to 
the  time  needed  for  adsorption,  so  that  the  new  surface  will  be  stronger 
than  the  old.  Likewise,  when  water  has  been  modified  by  a  relatively 
insoluble  contaminant,  the  components  of  the  film  can  so  dispose  them- 
selves that  the  surficial  forces  will  be  the  same  everywhere,  that  is,  they 
tend  to  remain  in  equilibrium,  including  the  force  of  gravity,  which 
otherwise  would  pull  them  apart.  Thus  the  tension  at  the  surface  of 
a  contaminated  liquid  is  able  to  adjust  itself  within  fairly  wide  limits, 
and  a  film  made  of  such  a  liquid  can  remain  in  equilibrium,  whereas 
a  film  of  pure  liquid  breaks  at  once.  A  soap-bubble  will  last  for  hours, 
a  pure-water  bubble  persists  for  the  fraction  of  a  second.  Moreover,  the 
presence  of  a  contaminant  in  water  may  also  affect  its  viscosity,  or 
internal  friction,  whereby  it  offers  resistance  to  change  of  shape.  This 
strengthens  the  film  of  a  bubble  generated  in  modified  water.  It  has 
been  asserted19  that  a  concentration  of  the  contaminant  occurs  at  the 
surface  of  such  a  liquid,  causing  the  viscosity  to  be  magnified  as  com- 
pared with  the  body  of  the  liquid.  This  statement  is  well  founded. 

An  interesting  experiment20  to  illustrate  this  phase  of  the  subject 


ifPoynting  &  Thompson,  op.  cit.,  page  137. 

isHildebrand.  Fig.  2,  page  169,  M.  &  S.  P.,  July  29,  1916.  Also  Willard 
Gibbs'  'Thermodynamics,'  page  313. 

i9Samuel  S.  Sadtler,  in  Minerals  Separation  v.  Miami  suit,  1915.  Em- 
phasized recently  in  the  Butte  &  Superior  case. 

2oHow  variously  it  can  be  seen  and  interpreted  is  shown  by  the  descrip- 
tions given  by  Messrs.  Durell,  Norris,  and  Rickard,  in  'The  Flotation  Process,' 
pp.  137,  315,  358;  also  by  Messrs.  Taggart  and  Beach  in  Trans.  A.  I.  M.  E., 
September  1916. 


PRINCIPLES   OF   FLOTATION  53 

can  be  made  by  floating  kerosene  over  blue-colored  water  and  then 
passing  air  into  the  lower  liquid.  When  bubbles  are  formed  in  the 
oil,  they  are  short-lived,  but  they  last  long  enough  to  indicate  that  the 
oil  is  not  a  pure  and  perfectly  homogeneous  liquid.  In  such  a  liquid, 
the  bubble  would  break  on  arrival  at  the  surface.  The  fact  that  two 
bubbles  touch  without  coalescing  (K,  K,  Fig.  14)  proves  that  there  is 


~    '  ~ 


~_    —  _-CU     _          _          _-       __ 


CO    E    r 

—     _       __-    _     *V  - 


-     -__-    °T  -      -._  TJ 


V   - 


a rj  


±a--A*:--- 


FIG.  14 

a  film  of  variable  composition  between  them.  When  I  blow  air  gently 
into  the  colored  water,-1  the  bubbles  that  rise  into  the  oil  are  colorless. 
They  accumulate  at  the  upper  surface  of  the  oil,  where  they  show  an 
attraction  for  each  other  and  also  for  the  sides  of  the  glass  vessel. 
They  last  longer  than  the  bubbles  blown  in  oil  because  they  are  made 
out  of  a  liquid  containing  a  decided  contaminant,  the  dye.  Next,  I 
blow  air  more  energetically,  and  I  note  that  when  the  bubble  is  about 
to  escape  from  the  blue  water  it  raises  the  surface  into  a  mound  (A  in 


21  Some  of  these  experiments  may  seem  almost  childish  to  the  supercilious, 
but  I  can  commend  them  not  only  as  giving  insight  into  fundamental 
principles  but  as  likely  to  stimulate  thoughtful  discussion. 


54  "FLOTATION 

Fig.  14),  emerging  at  the  point  of  it  (as  at  B)  as  if  the  air  had  dragged 
the  water  in  an  effort  to  overcome  a  viscous  layer.  This  indeed  is  the 
fact.  I  caught  one  bubble  in  the  act ;  it  came  slowly  through  the  little 
heap  of  water  and  remained  poised  at  the  top  of  the  mound,  finally 
breaking  away,  while  the  water  subsided  sluggishly  to  its  level. 
Finally,  I  introduced  air  more  rapidly  into  the  water.  The  bubbles 
broke  through  the  viscous  water-oil  interface  and  carried  portions  of 


-       —**    -  OF   -     - 


FIG.  15 

water  with  them.  These  portions  slipped  from  the  north  (B,  B)  to  the 
south  pole  (F,  F)  of  the  bubbles  and  fell  away,  sometimes  not  until 
the  bubbles  had  reached  the  upper  surface  of  the  oil.  An  intermediate 
stage  is  shown  by  C,  C.  This  water  that  detached  itself  from  the  air- 
bubble  was  not  a  stable  film  but  a  viscous  coating.  It  assumed  various 
forms,  crescent,  hemispherical  (D,  Z>),  lenticular,  flatly  globular 
(E,  E),  or  even  shapeless  (G).  The  retention  of  a  form  that  is  not 
spherical  is  proof  that  the  force  of  surface-tension  is  overcome  by  the 
high  viscosity  of  the  film  at  the  water-oil  interface.22  Occasionally 


22As  elucidated  recently  by  A.  F.  Taggart  in  the  Butte  &  Superior  case. 


PRINCIPLES   OF    FLOTATION  55 

some  of  the  blue  water  remains  as  a  globule  attached  to  the  surface  of 
the  oil,  as  at  8.  On  reaching  the  oil-water  interface  the  globule  (as 
at  W)  will  merge  itself  slowly  with  the  liquid  from  which  it  originated. 

If  a  similar  experiment  is  made  with  carbonated  water,  in  which 
minute  bubbles  of  nearly  equal  size  are  generated  quickly,  one  can  see 
the  little  bubbles,  like  bright  colorless  beads,  leading  a  much  bigger 
globule  of  blue  water  upward  (as  at  A',  A'  in  Fig.  15)  through  the 
oil  to  the  surface,  where  the  bubble  breaks  and  the  globule  of  water 
falls  back  through  the  oil  in  oblately  spheriodal  shape  (B,  B).  Some- 
times two,  or  even  three,  couples  rise  tandem  (as  at  A"  and  A'"}.  At 
the  surface  of  the  oil  the  coalescence  of  several  bubbles  may  leave  one 
large  bubble  to  which  several  small  globules  of  water  are  attached  (as 
at  C),  or  globules  of  blue  water  (D)  may  remain  floating  in  the  oil, 
as  if  hanging  from  the  surface  of  it.  Sometimes  the  bubble  may  be 
over-weighted  and,  after  rising  a  little  way,  it  descends  (K).  If  the 
couples  collide,  the  bubbles  are  released  and  leave  their  freight  of 
water,  which  drops  back.  The  interesting  feature  is  the  air-bubble's 
ability  to  lift  a  water-globule  so  much  larger  than  itself.  This  is  due 
to  the  fact  that  the  water  comes  from  the  water-oil  interface  and  in- 
cludes oil. 

The  amount  of  the  contaminant  in  the  froth  of  a  flotation-cell  can 
be  measured  by  analysis.  The  concentration  in  a  film  may  proceed  so 
far  as  to  form  a  solid,  as  when  using  hard  water.  The  use  of  oil  as  a 
modifying  agent  is  advantageous  because  it  is  not  prone  to  enter  into 
chemical  reactions  with  impurities  in  the  mill-water  even  when  thus 
concentrated  in  the  bubble-films;  otherwise  some  other  contaminant 
might  be  used.  Indeed,  it  is  likely  that  oil  will  be  replaced  by  some 
contaminant  that  is  cheaper  and  that  may  also  induce  some  desirable 
chemical  reaction.  Several  such  substitutes  are  now  being  tried  in 
flotation  plants. 

The  question  has  been  asked,  when  a  bubble  is  formed  in  a  liquid, 
is  it  a  spherical  hole  filled  with  gas  or  is  it  a  sac ;  in  short,  has  it  a 
skin  or  not?  The  reply  to  this  question  involves  the  whole  theory  of 
surface-tension  and  bubble-making.  When  a  pure  gas  is  blown  into 
a  pure  liquid,  the  bubbles  rise  rapidly  to  the  surface,  where  they 
burst  instantly.  The  gas  injected  into  the  liquid  is  subject  to  the  gas- 
liquid  tension,  therefore  the  surface  of  the  liquid  enclosing  the  portion 
of  gas  assumes  a  spherical  shape  in  obedience  to  that  tension,  because 
a  sphere  occupies  the  least  space.  The  liquid  in  contact  with  the  gas 
will  have  a  different  orientation  of  its  molecules  and  it  will  be  slightly 
denser  than  the  internal  liquid.  These  conditions  will  accompany  the 


56  FLOTATION 

globule  of  gas  in  its  passage  upward.  The  form  of  the  liquid  periphery 
persists  but  the  substance  of  the  liquid  in  contact  with  the  gas  is  chang- 
ing as  the  bubble  rises.  An  analogy  is  furnished  by  the  motionless 
cloud  on  a  mountain.  The  cloud  retains  its  shape,  although  its  sub- 
stance is  fleeting.  Ascend  the  mountain  and  you  find  yourself  sur- 
rounded by  a  mist  that  is  traveling  at  the  rate  of  20  or  30  milts  per 
hour,  or  even  faster;  yet  as  seen  from  the  valley  the  cloud  seems  fixed. 
The  explanation  is  that  the  moisture-laden  air  sweeps  into  the  cold 
area  on  one  side,  either  the  snowy  or  shady  side  of  the  peak,  and  there 
the  moisture  is  condensed  to  globules  of  water  constituting  a  fog  or 
mist ;  these  are  visibly  driven  forward,  to  be  expanded  suddenly  and 
dissipated  into  clear  air  as  soon  as  they  pass  beyond  the  cold  area,  but 
their  place  is  taken  by  others  coming  on  behind,  so  the  shape  of  the 
cloud  persists  although  the  substance  of  it  is  rushing  forward  at  the 
speed  of  a  railway-train. 

Now  the  important  question  arises:  What  is  the  substance  of  the 
film  of  the  bubble  as  it  passes  from  one  liquid  into  another?  The 
attachment  of  blue  water  to  the  bubble  in  the  water-oil  experiment  is 
confusing,  because  it  obscures  the  fact  that,  as  the  coating  of  water 
slips  away,  the  bubble  acquires  an  oily  film  and  when  temporarily  at 
rest  on  the  surface  it  is  enveloped  in  an  oily  film.  No  blue  tinge  can 
be  detected,  if  the  effect  of  reflection  from  below  be  avoided.  On  the 
other  hand,  if  the  experiment  be  repeatd  with  heavy  oil  (colored  by 
'oil  orange')  and  alcohol,  it  will  be  found  that  the  bubbles  that  come  to 
roost  at  the  upper  surface  of  the  alcohol  are  orange-colored.  Thus,  as 
scientific  theory  would  suggest,  the  bubbles  take  a  film  of  the  liquid 
having  the  lower  surface-tension  or  less  molecular  cohesion.  In  pass- 
ing from  water  to  oil  or  from  oil  to  alcohol  the  bubble  has  an  oily 
film  at  the  end  of  its  journey.  If  a  bubble  were  generated  in  water 
and  passed  successively  through  oil  and  alcohol,  it  would  have  a  water, 
oil,  and  alcohol  film  in  sequence.  If  the  bubble  passed  in  the  reverse 
direction  it  would  have  an  alcoholic  film  in  the  alcohol,  the  oil,  and  the 
water  alike,  because  alcohol  spreads  over  oil  and  oil  spreads  over 
water,  the  liquid  having  the  less  cohesion  or  surface-tension  being 
pulled  by  the  molecular  attraction  of  the  liquid  having  the  stronger 
cohesion  or  surface-tension.  There  is  this  to  be  added,  however,  that 
the  bubble  generated  in  water  would  have  some  water  in  its  oily  film 
when  in  the  oil,  and  some  oil  in  its  alcoholic  film  when  in  the  alcohol. 
Each  liquid  in  turn  serves  slightly  to  contaminate.  On  the  return 
journey,  the  alcoholic  film,  contaminated  slightly  by  the  air  and  by  any 
impurity  in  the  alcohol-air  interface,  would  resist  modification  by  the 


PRINCIPLES   OF    FLOTATION  57 

oil  and  by  the  water  (forming  the  lower  layers  of  liquid)  because  the 
alcohol  would  spread  over  both  the  oil-air  interface  and  the  water- 
air  interface.  Imagine  a  globule  of  oil  in  an  air-bubble  enclosed  by 
water  (Fig.  16)  :  the  oil  spreads  and  forms  a  film  to  enclose  the  air. 

01  L 


WATELR  OIL 

FIG.  16 

Now  imagine  a  globule  of  water  in  an  air-bubble  surrounded  by  oil; 
the  water  does  not  spread,  because  the  pull  of  the  air-water  and  water- 
oil  surfaces  is  greater  than  that  of  the  oil-air  surface;  therefore  a 
water-filmed  bubble  will  acquire  an  oil  film  when  passing  into  oil ;  on 
the  other  hand  an  oil-filmed  bubble  will  retain  its  film  in  making  the 
same  entry  through  water. 

We  have  seen  that  mineral  has  a  selective  adsorption  for  oil  rather 
than  for  water  and  that  in  this  respect  it  differs  from  gangue.  Metallic 
particles  adsorb  air,  but  this  fact  is  relatively  unimportant  in  flotation 
because  the  air  approaches  them  when  it  is  enclosed  within  a  liquid 
envelope  that  is  contaminated  by  oil.  Therefore  the  adhesion  of  oil  for 
the  metallic  surface  becomes  the  dominant  factor.  The  older  notion 
that  the  affinity  of  air  for  metallic  surfaces  played  an  important  part 
in  flotation  has  been  set  aside,  because  of  the  absence  in  the  flotation- 
cell  of  any  direct  contact  between  air  and  mineral.  Metallic  surfaces, 
such  as  those  of  minerals,  are  supposed  to  adsorb  air  and  that  is  why 
they  are  not  readily  wetted.  It  may  be  due  to  molecular  density, 
coupled  with  reduction  of  inter-molecular  distance,  which  is  practic- 
ally the  same  thing  as  a  reduction  of  sub-capillary  porosity.  Adsorp- 
tion of  air  would  also  bear  a  relation  to  the  higher  density  of  the 
mineral.  Such  adsorption  plays  its  part  in  the  older  surface-tension 
processes,  such  as  those  of  Wood  and  Macquisten,  but  in  the  later 
flotation  processes  there  is  present  insoluble  oil  or  a  soluble  frothing 
agent,  and  this  renders  it  impossible  for  the  globule  of  air  to  come  into 
direct  contact  with  the  mineral.  It  is  not  the  air,  but  the  film  around 
it,  that  provokes  the  attachment  of  the  bubble  to  the  mineral. 

Now  let  us  consider  the  air-bubble  made  in  water  containing  an 


58  FLOTATION 

impurity  that  decreases  its  surface-tension.  In  the  language  of  flota- 
tion we  would  say  that  this  impurity  is  a  contaminant  modifying  the 
water.  As  soon  as  the  air  enters  the  water  it  assumes  a  globular  form 
as  before,  but  when  the  bubble  reaches  the  surface  it  persists;  it 
does  not  burst  at  once.  The  bubble  in  the  water  is  a  spherical  hole 
occupied  by  air ;  the  air  has  displaced  the  water  and  is  enclosed  by  it ; 
the  water-surface  in  contact  with  the  air  is  in  a  state  of  tension  as 
compared  with  the  interior  body  of  water,  and  that  causes  contraction 
into  spherical  shape.  The  surface-tension  has  been  lowered  by  the  con- 
taminant so  that  the  bubble-film  is  in  a  state  of  less  strain  than  a 
similar  film  of  pure  liquid,  hence  a  diminution  in  the  tendency  to  con- 
tract and  to  collapse.  Moreover  there  is  a  tendency  for  the  contami- 
nant, whatever  it  be,  to  concentrate  at  the  air-water  surface ;  there  is 
a  differentiation  of  the  constituents  of  the  liquid,  causing  the  surface 
to  differ  slightly  in  composition  from  the  bulk  of  the  solution  and  so 
to  accentuate  the  modification  due  to  the  presence  of  the  impurity. 
The  bubble-film  or  air-liquid  contact  adsorbs  the  contaminant  until 
equilibrium  is  established,  and  the  contaminated  liquid  of  the  film 
carries  some  of  the  contaminant  all  the  way  to  the  surface,  despite 
the  interchange  between  molecules  or  particles  of  the  contaminant  on 
the  way  up.  This  differentiation  and  concentration  of  the  contam- 
inant at  the  surface  of  the  water  in  contact  with  the  air-bubble  may 
indeed  be  likened  to  a  film  *or  membrane,  so  that  the  bubble  may  be 
regarded  as  a  sac,  but  it  is  a  sac  the  substance  of  which  is  not  fixed 
while  the  bubble  is  moving  upward  through  the  water.  It  cannot  be 
regarded  as  enclosed  within  a  definite  film  until  it  reaches  the  end  of 
its  journey,  and  even  then  the  film  is  coterminous  with  the  surface 
at  which  it  rests,  and  the  play  of  light  upon  it  shows  that  the  re- 
arrangement of  its  substance  is  still  in  progress,  as  the  excess  of 
liquid  drains  to  the  south  pole.  The  variability  in  the  surface-tension 
due  to  the  shifting  of  the  contaminating  particles  is  essential  to  the 
longevity  of  the  bubble-film.  That  brings  us  to  a  recognition  of  an 
important  factor:  viscosity. 

VISCOSITY.  This  is  defined  as  the  internal  friction  of  a  liquid  or 
its  resistance  to  a  change  of  shape.  Two  years  ago  the  part  played  by 
viscosity  in  establishing  a  bubble-film  was  subordinated  to  emphasis  on 
the  lowering  of  the  surface-tension  of  the  water. in  the  ore-pulp.23 


-'•'^However,  I  pointed  to  the  probability  of  viscosity  contributing  to  the 
tenacity  of  the  film,  even  in  the  needle  experiment  on  tap-water,  and  quoted 
Boys  to  show  that  increase  of  viscosity  was  involved  in  the  lowering  of  sur- 
face-tension in  enabling  a  bubble  to  persist.  M.  &  S.  P.,  Sept.  11,  1915,  p.  385. 


PRINCIPLES   OF    FLOTATION 


51) 


60  FLOTATION 

Since  then  this  branch  of  the  theory  has  been  elucidated  by  Messrs. 
Taggart,  Beach,  and  Bancroft.24 

The  addition  of  alcohol  increases  the  viscosity  of  water  up  to 
about  47%,  after  which  the  further  addition  decreases  the  viscosity. 
Alcohol,  of  course,  lowers  the  surface-tension  of  water,  but  an  ex- 
periment25 will  prove  that  the  change  of  viscosity  is  the  dominant 
factor  in  making  a  froth.  If  alcohol,  to  which  5%  water  has  been 
added,  be  stirred  violently  in  the  glass- jar  machine  familiar  to  flota- 
tionists  there  will  be  no  formation  of  froth,  but  if  the  experiment  be 
repeated  with  tap-water,  to  which  1%  of  alcohol  is  added,  then  a 
froth  is  produced  at  once. 

Such  an  alcohol-water  froth  is  non-persistent,  because  the  absolute 
viscosity  is  low.  To  increase  it  we  must  have  a  colloidal  suspension ; 
for  example,  the  foam  on  beer.  The  colloidal  protein  of  beer  yields 
a  froth  that  lasts  longer  than  the  bubbles  on  champagne,  which  are 
short-lived,  like  the  alcohol-water  foam  of  the  experiment  just  de- 
scribed. To  obtain  a  froth  sufficiently  persistent  to  serve  a  metallurgic 
purpose  it  is  necessary  to  increase  the  viscosity  of  the  bubble-films. 
This  is  one  of  the  functions  of  the  oil,  and  it  is  one  that  follows  upon 
its  affinity  for  metallic  surfaces.  It  adsorbs  or  concentrates  (at  the 
surface  of  the  bubbles)  the  mineral  particles  in  the  pulp  so  as  to 
form  an  interface  that  is  more  viscous  than  either  the  oil  or  the 
water  or  the  mixture  of  the  two.26  It  is  the  presence  of  solid  matter 
that  contributes  to  the  viscosity  of  the  bubble-films  in  the  froth. 

If  a  needle  be  floated  on  water  by  means  of  a  raft  made  of  wooden 
matches  and  if  a  chip  of  wood  be  floated  to  one  side  of  it,  one  can  use 
a  magnet  to  turn  the  raft  and  needle  on  the  surface  of  the  water 
without  moving  the  chip.  This  shows  that  the  surface,  or  water-air 
interface,  has  no  noticeable  viscosity.27  If,  however,  the  surface  be 
dusted  with  finely  pulverized  ore,  then  the  magnet  will  cause  the 
chip  to  move  with  the  rafted  needle.  The  viscosity  has  been  so  greatly 
increased  by  the  addition  of  solid  matter  to  the  interfacial  film  that 
the  surface  behaves  as  if  it  were  solid.  Next,  if  a  drop  of  oil,  sufficient 
to  lower  its  surface-tension,  be  added  to  the  water,  the  chip  will  not 
turn  when  the  rafted  needle  is  moved  by  the  attraction  of  the  magnet. 


24More  particularly  in  their  expert  testimony  at  Butte,  from  which  I 
have  quoted  already. 

ssDescribed  by  Wilder  D.  Bancroft  in  his  testimony  at  Butte. 

seTaggart. 

27Taggart.  He  pointed  to  the  fact  that  the  addition  of  the  oil  increased 
the  viscosity  of  the  surface  so  as  to  cause  it  to  act  as  a  solid  within  small 
distances,  close  to  the  raft,  but  considerably  less  than  when  the  powdered 
ore  was  sprinkled  upon  the  oiled  surface. 


PRINCIPLES   OF    FLOTATION 


61 


62  FLOTATION 

Such  increase  of  viscosity  as  has  been  caused  by  the  oil  is  insufficient 
to  form  a  resisting  medium.  Finally,  if  powdered  ore  is  dusted  upon 
the  oil-contaminated  surface,  again  the  chip  does  not  move  with  the 
raft,  because  "the  surface  has  been  stabilized  and  made  highly 
viscous."-8 

If  water  and  kerosene  be  poured  successively  into  a  glass  bottle, 
and  if  then  finely-divided  copper,  called  'bronze  powder',  be  intro- 
duced and  the  contents  of  the  bottle  be  subjected  to  vigorous  shaking, 
and  then  allowed  to  remain  quiescent,  the  copper  powder  collects  at 
the  oil-water  interface  and  from  it  slowly  a  bronze  film  will  separate 
itself  and  become  pendant.  This,  when  viewed  by  transmitted  light, 
is  seen  to  be  a  lace-like  fabric,  like  a  cobweb  that  has  been  long  ex- 
posed to  dust.29  It  is  a  film  of  particles  of  kerosene  and  water  so 
viscous,  owing  to  the  inclusion  of  the  powdered  copper,  that  it  hangs 
like  a  curtain ;  it  is  an  adsorption  layer  of  bubble-film  matter  hanging 
from  the  oil-water  interface.  The  presence  of  the  powdered  copper 
has  stabilized  the  film. 

It  is  important  to  note  that  such  increase  of  viscosity  as  prolongs 
the  life  of  the  bubble-film  need  not  be  metallic.  When  pine-oil  is 
added  to  water,  and  the  mixture  is  agitated,  the  froth  that  comes  to 
the  surface  of  the  water  is  thin  and  evanescent.  When  to  this  there 
is  added  lycopodium  powder,  which  is  of  vegetal  origin,  being  the 
spores  of  club-moss,  the  froth  becomes  thick  and  lasting.30  If  the 
lycopodium  be  used  without  the  pine-oil,  no  persistent  froth  is  made. 
In  this  case,  as  with  the  bronze  powder,  the  effect  of  the  solid  is  to 
stabilize  the  froth  by  making  the  bubble-films  more  viscous.  The 
gangue  would  serve  for  this  purpose  if  the  particles  of  gangue  could 
pass  into  the  oil-water  interface,  but  it  happens,  as  we  have  seen, 
that  the  oil  exhibits  a  choice  for  the  particles  of  mineral,  so  that  they 
are  adsorbed  preferentially. 

Another  experiment:31  When  a  needle  was  floated  on  water  in  a 
beaker  and  a  drop  of  caster-oil  was  added,  the  needle  did  not  sink. 
When  another  drop  of  the  same  oil  was  added,  the  globule  moved  to 
the  needle  and  adhered  to  it.  But  it  continued  to  float.  When  a  drop 
of  pine-oil  was  allowed  to  run  down  the  side  of  the  beaker,  the  needle 
sank  as  soon  as  the  pine-oil  touched  the  water,  while  the  globule  of  oil 


281  am  quoting  from  Mr.  Taggart's  testimony,  from  which  the  description 
of  the  experiment  also  is  taken. 

29P.  E.  Beach,  who  performed  the  experiment  in  the  court-room  at  Butte. 
R.  B.  Yerxa  repeated  it  for  me  at  Miami. 

soBancroft,  who  performed  the  experiment  in  the  court-room  at  Butte. 

•!iMade  for  me  by  Mr.  Yerxa  in  the  laboratory  at  Miami. 


PRINCIPLES   OP    FLOTATION 


63 


remained  afloat.  Apparently  the  increase  of  viscosity  due  to  the  thick 
oil  counteracted  the  lowering  of  the  water's  surface-tension. 

The  effect  of  saponine,  noted  in  Hoover's  hook  as  being  so  detri- 
mental to  flotation,  can  now  he  explained.  Although  it  does  not  in- 
crease the  surface-tension  of  water,  but  tends  rather  to  decrease  it 
very  slightly,  according  to  Freundlich,  it  causes  a  marked  increase  of 
viscosity.  The  result  is  a  good  froth ;  but  it  exhibits  no  essential  ad- 
hesion, that  is,  the  saponine  solution  is  not  adsorbed  by  the  mineral. 
Therefore  the  froth  does  not  persist  and  the  mineral  is  not  floated. 

Any  substance  that  is  adsorbed  into  the  oil,  or  the  oil-water  inter- 
face, of  the  bubble  will  pass  into  the  film.  If  it  does  that  the  sub- 
stance will  be  floated.  Mineral  goes  into  oil  in  preference  to  gangue. 


FIG.  19 


If  a  particle  of  sulphide  is  in  the  vicinity  of  oil  and  water,  the  oil- 
surface  of  the  sulphide  grows  larger  and  the  water-surface  grows 
smaller,  until  the  sulphide  at  the  last  takes  a  position  within  the  oil. 
Reversely,  a  particle  of  quartz  takes  a  position  within  the  water.  The 
greatest  possible  area  of  sulphide  that  can  be  covered  by  the  oil  is  when 
the  sulphide  is  within  the  oil ;  therefore  the  particles  of  sulphide  tend 
to  encase  themselves  within  the  oily  substance  of  the  bubble-film  and 
so  not  only  stabilize  it  but  give  themselves  the  opportunity  of  being 
floated  to  the  surface  in  the  froth. 

OIL-FILMS.  In  the  course  of  the  first  trial  of  the  Miami  lawsuit,  at 
Wilmington,  a  series  of  demonstrations  was  made  in  court  for  the  pur- 
pose of  argument.  These  experiments  were  photographed  and  placed 
in  the  record.  Some  of  them  are  of  scientific  interest.  Fig.  19  shows 
the  curved  pipette  employed  to  pass  an  air-bubble  to  the  bubble-holder, 
which  is  a  bell-mouthed  glass  tube.  Fig.  20  shows  the  play  of  a 


64  FLOTATION 

bubble  on  the  oil  placed  upon  a  particle  of  galena  lying  at  the  bottom 
of  a  vessel  containing  water.  In  A  the  particle  of  galena  and  the 
bubble-holder  are  shown.  In  B  a  globule  of  oil  rests  on  the  galena. 
The  oil  is  1^  times  the  volume  of  the  galena  particle.  In  C  the  air- 
bubble  is  adhering  to  the  oil  on  the  galena  and  drawing  it  up,  forming 
a  neck  of  oil  between  the  bubble  and  the  galena.  The  photographs 
exhibit  the  affinity  of  the  oil  for  the  air-bubble.  If  the  bubble  failed  to 
raise  the  particle  of  galena,  this  should  not  occasion  surprise,  as  it 
was  much  too  large — several  thousand  times  bigger  than  the  average 
pulp  treated  in  notation.  In  Fig.  21  similar  experiments  on  particles 
of  unoiled  galena  of  a  reasonable  size — about  20  mesh — are  recorded 
photographically.  In  the  first  of  this  serie's  the  bubble-holder  is  ap- 
proaching one  of  three  particles,  in  the  second  it  is  moving  away  with 
one  of  them,  and  in  the  third  with  another.  In  Fig.  22  another  series 
of  experiments  is  shown,  but  with  oiled  particles  of  galena,  of  plus 
20-mesh  size.  In  the  third  member  of  this  group  it  will  be  noted  that 
all  the  galena  particles  are  being  carried  away  by  the  bubble.  Two 
of  these  particles  are  adhering  to  the  third  particle,  which  is  attached 
directly  to  the  bubble.  Ordinary  tap-water  was  used.  These  experi- 
ments, and  others  like  them,  showed  that  particles  of  galena  will  adhere 
to  an  air-bubble,  whether  they  are  oiled  or  not.  The  adhesion  takes 
place  even  when  the  mineral  carries  an  excess  of  oil.  Particles  of 
chalcocite  do  not  adhere  so  readily  to  the  air-bubble  when  they  are 
unoiled  as  when  they  are  oiled,  but  the  evidence  given  in  this  suit  was 
incomplete ;  moreover,  it  was  not  shown  whether  a  bubble  made  out  of 
water  suitably  modified  will,  or  will  not,  adhere  to  an  unoiled  particle 
of  chalcocite.  The  motion-pictures  of  these  demonstrations  cost  a 
great  deal  of  money,  but  it  will  be  acknowledged  now,  I  believe,  that 
they  threw  but  little  light  on  the  theory  of  flotation. 

The  adhesion  of  air,  as  a  bubble  in  water,  to  mineral  particles  is 
easy  enough  to  prove,  but  such  bubbles,  as  far  as  I  have  been  able  to 
ascertain  by  experiments,  will  adhere  to  almost  anything  that  happens 
to  be  near-by.  Trying  some  of  these  experiments  recently  with  Mr. 
Yerxa,  at  Miami,  I  found  that  a  large  air-bubble  would  not  lift  an 
8-mesh  particle  of  chalcocite  without  a  good  deal  of  coaxing,  but  when 
a  minute  (accidental)  air-bubble  became  poised  on  the  chalcocite  then 
the  big  bubble  attached  itself  to  the  small  one  and  thereby  raised  the 
mineral  particle.  When  the  chalcocite  was  oiled  the  bubble  was  lifted 
without  hesitation.  Examining  the  bubble-film,  it  will  be  seen  (Fig. 
23  that  the  particle  of  chalcocite  hangs  from  it  when  in  the  water, 
but  as  soon  as  the  bubble  is  taken  out  of  the  water  into  the  air,  the 


PRINCIPLES   OF    FLOTATION 


65 


tt 


66 


FLOTATION 


^BBmm 

I 


PRINCIPLES   OF    FLOTATION 


67 


c 

FIG.  22 


68 


FLOTATION 


chalcocite  is  enclosed  between  an  inner  and  an  outer  surface,32  in  both 
of  which  the  oily  contaminant  is  so  concentrated  as  to  form  an  ad- 
sorption layer. 

The  nature  of  this  oil-water  interface  is  indicated  by  another  ex- 
periment. If  water  and  pine-oil  are  poured  successively  into  a  test- 
tube  and  a  particle  of  chalcocite  is  dropped  into  it,  we  shall  find  (Fig. 
24)  the  particle  floating  at  the  oil-water  interface  in  such  a  way  that 


f/L  M  IN 

CHAi-COCiTE      /j/f? 


FIG.  23 


the  mineral  seems  to  be  in  the  water,  when  it  is  really  enclosed  within 
a  downward  protrusion  of  the  oil. 

When  a  bubble  is  in  oily  water  it  has  only  one  contaminated  sur- 
face, or  adsorption  layer,  but  when  it  emerges  it  has  two.     See  Fig. 


01  L 


FIG.  24 


25.    The  oil  is  concentrated  at  the  surfaces  in  contact  with  the  air,  out- 
side and  inside,  leaving  the  less  modified  water  between. 

Again,  when  a  globule  of  pine-oil  was  placed  on  the  smooth  sur- 
face of  a  lump  of  chalcocite  under  water,  the  pine-oil  was  held  by  the 
chalcocite  as  against  a  bubble  brought  in  contact  with  it,  but  when  the 
globule  of  oil  lay  on  a  piece  of  quartz  the  pine-oil  was  adsorbed  by  the 
bubble.  A  particle  of  mineral  and  a  bubble  show  mutual  attraction 
and  if  the  mineral  particle  is  minute  it  becomes  drawn  into  the  inter- 
face of  the  bubble-film.  That  may  be  why  larger  particles  are  not 


32As  elucidated  by  Taggart  at  Butte. 


PRINCIPLES   OF   FLOTATION  69 

floated  easily ;  they  are  too  big  to  be  enveloped  in  this  way.  The  min- 
eral particles  are  carried  within  the  bubble-film ;  they  are  not  attached 
to  it  outside.  That  may  explain  why  fine  pulverization  is  essential  to 
the  success  of  flotation.  Thus  we  arrive  at  the  idea  that  it  is  not  the 
air  in  the  bubble  only,  but  the  nature  of  the  film,  that  affects  the  float- 
ability  of  the  metallic  particles. 

The  addition  of  oil  to  water — in  a  beaker,  for  example — causes  an 
oily  film  to  appear  at  the  interface  between  water  and  air.  When  an 
air-bubble  meets  an  oil-glouble  they  will  be  mutually  attracted  and 


some  of  the  oil  will  pass  into  the  interface  between  water  and  air. 
When  air  occupies  a  hole  in  water,  forming  what  is  called  a  bubble, 
the  periphery  of  this  hole  presents  a  surface — exposed  to  the  air 
within — like  the  surface  of  the  water  in  the  beaker.  In  each  case  the 
oil  tends  to  concentrate  at  that  air-surface. 

The  old  idea  that  the  mineral  particle  attached  itself  directly  to  air 
is  now  relegated  to  one  side ;  while  this  mutual  attraction  may  exist, 
it  plays  a  minor  part  because  the  air  when  it  approaches  the  mineral 
in  a  pulp  is  always  enclosed  within  a  watery  film  contaminated  by  oil 
or  some  substance  that  functions  similarly.  This  statement  has  been 
made  previously  and  is  repeated  here  for  emphasis. 

It  has  been  disclosed  by  microscopic  examination33  that  the  mineral 
particle  is  not  in  direct  contact  with  air,  but  so  enclosed  within  the 
film  as  not  to  be  in  touch  with  air  either  inside  or  outside  the  bubble 
in  a  mass  of  froth.  The  film  raises  itself  over  the  particle  and  wraps 
itself  under  the  particle,  so  that  the  mineral  is  enclosed  within  a 
watery  interspace.  The  film  itself  consists  of  an  exterior  surface  in 


s«Taggart. 


70  FLOTATION 

which  the  oil  is  concentrated,  and  of  an  interior  surface  in  which  oil 
also  is  concentrated,  both  of  these  oily  concentrations  grading  toward 
the  water  that  lies  between  them.  The  oil  is  concentrated  at  each 
gas-liquid  interface,  just  as  oil  concentrates  at  the  surface  of  water 
in  contact  with  the  atmosphere. 

The  various  experiments  described  in  the  foregoing  pages  have 
shown  that  the  oil  in  a  pulp,  consisting  of  crushed  ore  and  water, 
performs  three  distinct  functions : 

1.  It  lowers  the  surface-tension  of  the  water. 

2.  It  assists  in  the  selection  of  the  mineral  particles. 

3.  It  promotes  the  formation  of  a  stable  froth. 

Water  is  a  convenient  liquid  for  flotation  work  because  it  has  a 
surface-tension  so  high  that  the  addition  of  almost  any  other  liquid 
will  lower  it.  The  lowering  of  the  surface-tension  diminishes  the  con- 
tractile force  in  water  and  lengthens  the  life  of  the  bubbles  that  are 
formed  by  the  injection  of  air;  but  this  lowering  of  the  surface-tension 
has  another  important  consequence :  it  creates  such  a  variable  con- 
centration of  oil  in  the  watery  film  of  the  bubble  as  to  enable  the  film 
to  adjust  its  strength  to  external  forces.  This  variability  of  tension 
is  even  more  important  than  the  lowering  of  the  surface-tension, 
because  it  serves  to  strengthen  the  film  where  necessary  by  lessening 
the  proportion  of  contaminant  at  any  weak  spot.  The  contaminant 
will  concentrate  at  the  surface  of  the  liquid  because  by  doing  so  it  will 
decrease  the  potential  energy. 

Next  conies  the  selective  adsorption  of  mineral  particles  by  the  oily 
film.  The  oil  wets  mineral  in  preference  to  gangue ;  it  envelopes  the 
mineral,  by  which  it  is  ' adsorbed'  or  attracted.  This  causes  the  par- 
ticles of  mineral  to  be  drawn  into  the  oily  film  of  the  bubbles,  which 
in  turn  are  strengthened  by  reason  of  the  increase  of  viscosity  im- 
parted to  their  films  by  the  inclusion  of  mineral  particles.  The 
electro-static  hypothesis  has  been  discarded  in  the  latest  investigations. 

Any  substance  that  will  lower  the  surface-tension  of  water  and  be 
adsorbed  by  mineral  particles  would  appear  to  promote  flotation.  The 
value  of  a  flotation  agent  depends  upon  its  ability  to  '  adsorb '  mineral. 
Most  brothers'  or  bubble-makers  by  themselves  are  not  satisfactory 
because  they  lack  this  ability,  and,  in  order  to  correct  the  deficiency, 
it  is  customary  to  add  a  'non-frothing'  oil,  which  is  adsorbed  strongly 
by  the  mineral,  thereby  promoting  successful  flotation.34  A  froth 
made  with  a  relatively  soluble  oil,  like  pine-oil,  can  be  stabilized  by 
adding  a  relatively  insoluble  viscous  oil,  like  fuel-oil.  The  idea  of 


^Bancroft.     In  his  testimony  at  Butte. 


PRINCIPLES   OF    FLOTATION  71 

agitation,  whether  of  the  violent  and  mechanical  kind  or  of  the  gentle 
and  pneumatic  kind,  is  to  bring  the  particles  of  mineral  in  contact 
with  the  oily  films  of  the  air-bubbles.  Whether  the  oil  is  emulsified 
before  or  after  it  is  added  to  the  pulp  does  not  matter  at  this  stage, 
but  the  oil  must  have  been  presented  to  the  bubbles  in  a  minutely  sub- 
divided condition,  so  that  they  may  acquire  oily  films  and  so  that  those 
films  may  come  in  touch  with  the  mineral  particles.  In  doing  so  the 
globules  of  oil  and  the  bubbles  that  they  contaminate  beneficially 
come  in  contact  with  particles  of  gangue  as  well  as  particles  of  min- 
eral, but  owing  to  the  tendency  of  oil  to  replace  water  at  the  surface  of 
the  mineral  particles  these  will  be  coated  with  oil  and  adsorbed  into 
the  oily  film  of  the  bubbles  and  rise,  whereas,  by  reason  of  the  tendency 
of  water  to  displace  oil  on  the  surface  of  gangue-particles,  those  will 
become  wetted  and  sink. 

'Mineral,'  'metallic,'  even  'ore,'  are  used  interchangeably  in  the 
technology  of  flotation.  The  misuse  of  'ore'  has  caused  great  con- 
fusion, for  the  object  of  the  process  is  not  to  recover  the  'ore',  but  only 
the  valuable  mineral  in  the  'ore,'  rejecting  the  valueless  portion, 
called  'gangue'.  As  between  'metallic'  and  'mineral,'  the  reference  is 
not  so  much  to  substances  containing  metals,  for  that  would  include 
much  of  the  gangue,  such  as  rhodonite  and  feldspar,  but  particularly 
to  minerals  having  a  metallic  lustre,  which  feature  appears  to  be 
favorable  to  the  adhesion  alike  of  air  and  oil.  'Sulphide'  is  another 
synonym,  because  the  sulphur  compounds  with  the  base  metals  are 
particularly  the  object  of  flotation,  but  'sulphide'  would  exclude  the 
tellurides.  At  least  one  sulphide  without  metallic  lustre  is  amenable 
to  flotation,  namely,  cinnabar.  So  is  graphite,  which  is  neither  sul- 
phidic  nor  metallic,  except  in  lustre.  Likewise  certain  forms  of 
scheelite  respond  to  flotation,  and  it  has  been  shown  by  experiment 
that  a  stable  froth  can  be  made  with  lycopodium  powder,  which  is  of 
vegetal  origin.  So  we  must  be  careful  in  our  use  of  terms.  The  use 
of  'metallic'  and  'mineral'  as  adjectives  to  designate  floatable  sub- 
stances is  based  on  a  concept  of  flotation  that  may  soon  be  discarded. 
No  classification  of  floatable  minerals  can  be  made  yet  and  when  it 
is  made  it  must  be  based  on  a  better  understanding  of  the  physical 
conditions  governing  flotation. 

The  amount  of  oil  required  in  froth-flotation  depends  upon  three 
factors:  the  proportion  of  mineral  to  be  concentrated,  the  amount  of 
water,  and  the  degree  of  aeration.  Air  and  water  are  needed  to  make 
bubbles ;  these  bubbles  must  be  oiled  in  order  that  they  may  engage  the 
mineral  in  the  pulp.  The  more  numerous  the  mineral  particles  the 


72  FLOTATION 

greater  the  number  of  oily  bubbles  needed  to  arrest  them.  If  the 
amount  of  water  is  doubled,  there  will  be  only  half  the  number  of 
mineral  particles  in  a  unit  of  space ;  therefore  more  oily  bubbles  will 
have  to  be  sent  in  search  of  them  than  if  they  were  herded  within  the 
smaller  volume  of  water.  The  idea  that  a  'critical'  proportion  of  oil- 
somewhere  under  1% — is  required  to  perform  successful  froth-flota- 
tion has  no  basis  of  evidence  outside  the  imaginings  of  a  group  of 
patentees  and  it  has  been  stultified  by  the  operations  of  1000-ton  plants 
using  22  or  23  pounds  of  oil  per  ton  of  ore,  in  Utah  and  Montana.  As 
Wilder  D.  Bancroft  has  said:  "The  hypothesis  of  a  'critical  point' 
rests  on  unverified  and  unverifiable  statements." 

THE  HYPOTHESIS.  Let  us  recall  the  principal  points  in  the  evi- 
dence before  venturing  upon  a  summary  of  our  conclusions.  I  write 
in  the  plural  advisedly,  for  the  evidence  has  come  from  many  sources 
and  the  suggestions  explaining  it  have  been  borrowed  from  many 
writers;  the  theory,  like  the. practice,  of  flotation  is  the  joint  work  of 
a  large  number  of  investigators. 

(1)  The  needle  that  floats  on   tap-water  will   sink   in   distilled 
water.     Although  contaminants  have  lowered  the  surface-tension85  of 
the  tap-water,  it  has  more  sustaining  power  on  account  of  its  aeration. 

(2)  The  bubble  blown  in  distilled  water  will  break  as  soon  as  it 
emerges,  but  the  solution  of  an  oily  substance  will  enable  a  boy  to 
blow  bubbles  that  sail  away  beautifully. 

(3)  The  addition  of  oil  lowers  the  surface-tension  and  thereby 
promotes  wetting,  but  the  adhesion  of  the  oil  to  the  surface  of  the 
mineral  particles  causes  the  water  to  be  displaced,  so  that  the  gangue 
preferably,  not  the  mineral,  is  wetted,  and  drowned. 

(4)  Emulsification  of  the  oil  provides  a  means,  through  the  sub- 
sequent breaking  of  the  emulsion,  for  imparting  oil  in  a  minutely  sub- 
divided state,  as  needed,  for  oiling  the  bubble-films  and  the  mineral 
particles. 

(5)  The  contaminant,  such  as  oil,  in  water  concentrates  at  the 
air-surface  and  by  doing  so  affords  a  surface-tension  sufficiently  vari- 
able to  be  adjustable  to  shock. 

(6)  The  oil-water  interface  is  more  viscous  than  the  body  of 
either  liquid. 

(7)  Oil  is  attracted  and  adsorbed  by  mineral  particles,  which 
therefore  are  pulled  into  the  oily  film  of  the  bubbles. 


3-r>The  layer  of  liquid  subject  to  surface-tension  has  a  thickness  less  than 
the  radius  of  molecular  action.  R.  S.  Willows  and  E.  Hatschek.  'Surface 
Energy,'  page  8. 


PRINCIPLES   OF   FLOTATION  73 

(8)  Bubbles  will  break  when  they  collide  unless  there  is  a  stable 
film  between  them,   preventing  coalescence.     Such  stability   is  fur- 
nished by  a  dissolved  substance  that  adjusts  the  surface-tension  and 
also  increases  the  viscosity  of  the  film. 

(9)  A  multiplicity  of  bubbles,  or  'froth/  will  serve  a  metallurgic 
purpose  if  it  floats  valuable  mineral  matter  long  enough  to  facilitate 
a  separation  from  the  valueless  components  of  the  pulp. 

The  recent  trend  of  hypothesis — it  has  hardly  the  status  of  a 
theory —  is  to  subordinate  sundry  ideas  prominent  a  year  ago.36  The 
direct  'adhesion'  of  air  to  mineral  particles  is  not  so  vital  as  was 
supposed,  because  air  and  mineral  rarely  come  in  direct  contact  in  the 
flotation  process;  usually  either  the  air-bubble  Has  an  oily  film  or  the 
mineral  itself  has  undergone  oil-filming.  The  lowering  of  the  surface- 
tension  of  water  is  still  a  fundamental  factor,  but  this  modification 
of  the  water  is  recognized  as  chiefly  important  not  for  the  first  conse- 
quence, which  promotes  the  wetting  of  the  mineral,  but  for  its  sec- 
ondary result,  which  is  to  create  a  variable  tension  on  the  surface  of 
a  bubble-film,  and  thereby  strengthen  it  greatly.  The  addition  of  acid 
has  ceased  to  be  essential,  it  having  been  found  that  alkaline  water 
is  better  for  the  treatment  of  many  ores.  The  acid,  like  the  oil,  is 
supposed  to  serve  more  than  one  purpose : 

(1)  To  adsorb  on  the  gangue  and  aid  the  wetting  of  it. 

(2)  To  promote  the  flocculation  of  gangue-particles  and  the  sepa- 
ration of  them  from  the  valuable  mineral. 

Fine  grinding  of  the  ore  is  recognized  as  necessary,  not  only  to 
separate  the  mineral  from  the  gangue,  but  to  assist  the  making  of  a 
froth  rich  in  mineral.  No  longer  is  the  mineral  supposed  to  be  buoyed 
by  the  bubbles,  as  if  tied  to  a  cork,  but  the  minute  particles  of  min- 
eral are  believed  to  be  drawn  into  the  bubble-film,  so  that,  to  pursue  the 
simile,  the  life-preserver  of  cork  surrounds  and  encases  the  thing  to 
be  floated.  The  idea  that  a  fixed  proportion  of  oil  to  'ore'  is  necessary 
has  gone  with  the  supposition  that  'oil'  only  will  perform  the  absorptive 
function  necessary  to  a  stable  froth.  Colloidal  sulphur,  sulphur  di- 
oxide, and  salt-cake  have  been  proved  effective  agents  in  froth-flota- 
tion ;  and  we  may  expect  a  steady  increase  in  the  discovery  of  such  sub- 
stances until  oil,  which  is  expensive,  is  discarded.  The  parts  played  by 
emulsification  and  by  the  formation  of  colloid  hydrates  are  becoming 
recognized  as  possibly  important  factors.  The  violent  type  of  agitation 
has  been  found  unnecessary,  and,  thanks  to  recent  litigation,*  it  is 


36'The  Flotation  Process,'  1916. 

*See  chapter  on  'Litigation'  elsewhere  in  this  volume. 


74  FLOTATION 

likely  that  the  use  of  compressed  air  under  low  pressure  will  supplant 
the  power-consuming  devices  of  an  earlier  period.  The  trend  is 
toward  simplicity  both  of  treatment  and  apparatus.  When  air  and  a 
cheap  modifying  agent  are  found  adequate  for  the  making  of  a  min- 
eral-bearing froth  then  the  flotation  process  may  be  deemed  fully 
developed. 


ATTENTION  may  be  drawn  to  the  interesting  statement  made  by  H. 
Hardy  Smith,  elsewhere  in  this  book,  that  natural  grease,  soluble  in 
ether,  was  detected  in  the  centre  of  a  large  uncracked  piece  of  sulphide 
ore  from  a  mine  at  Broken  Hill.  This  may  explain  T.  J.  Hoover's 
interesting  observation,  quoted  on  page  21  of  this  volume.  It  remains 
to  note  the  opinion  of  W.  E.  Simpson  that  the  natural  flotative  agent 
is  gelatinous  silica  formed  by  the  reaction  between  fluorspar  and 
quartz  with  the  hot  sulphuric  acid  used  in  the  Potter  process.  Such 
gelatinous  silica  is  said  to  have  a  selective  adhesion  for  lustrous  bodies, 
similar  to  those  of  oil  or  grease.* 


AMONG  recent  patents  for  flotation-agents  are  No.  1,228,183  and 
1,228,184,  of  May  29,  1917,  issued  to  Henry  P.  Corliss  for  the  use  of 
alpha-naphthylamine  and  nitro-naphthalene  respectively.  The  second 
of  these  is  non-oleagenious  and  solid,  but  it  can  be  dispersed  in  pulp  so 
uniformly  as  to  perform  its  frothing  function  most  effectively.  Only  a 
quarter  of  a  pound  is  needed,  as  used  at  the  Magma  mill,  where  also 
alpha-naphthylamine  has  reduced  the  copper  tailing  from  0.6  to  0.3% 
on  a  4  to  4£%  feed.f  This  may  prove  a  discovery  of  the  greatest  im- 
portance, because,  being  neither  '  on"  nor  'soluble',  these  substances  can 
be  used  without  conflict  with  the  basic  patents  of  the  Minerals  Separa- 
tion company. 


*'The  Potter  Process  at  Broken  Hill,'  W.  E.  Simpson.    M.  &  S.  P.,  May  26, 
1917. 

tM.  &  S.  P.,  July  14,  1917. 


TESTING  ORES  75 

TESTING  ORES  FOR  THE  FLOTATION  PROCESS 

By  0.  C.  RALSTON  and  GLENN  L.  ALLEN 

(Revised  from  the  Mining  and  Scientific  Press  of  January  1  and 
January  8,  1916) 

INTRODUCTION.  Although  the  subject  of  testing  for  flotation  has 
been  well  presented  in  T.  J.  Hoover's  book  on  'Concentrating  Ores  by 
Flotation/  there  is  need  of  later  information  on  this  timely  subject. 
Much  testing  has  been  done  in  laboratories  not  connected  in  any  way 
with  the  Minerals  Separation  company,  with  which  Mr.  Hoover  was 
formerly  associated  as  metallurgical  engineer,  and  there  have  been 
developed  methods  of  investigation  that  may  prove  suggestive  to  many 
experimenters. 

On  that  account  we  have  compiled  data  on  the  subject  of  testing 
both  from  the  literature  available  and  from  our  own  experience,  as 
well  as  from  what  we  have  seen  in  other  laboratories.  This  paper  is 
designed  to  present  the  results  of  this  compilation,  with  a  critical  dis- 
cussion of  the  more  important  methods  now  in  vogue. 

On  account  of  the  empirical  state  of  the  art  of  flotation  a  great  deal 
of  testing  is  necessary  before  large-scale  practice  can  be  commenced 
on  any  ore  -t  therefore  a  small  laboratory-machine  is  necessary  in  which 
many  tests  involving  many  variables  can  be  made  in  a  short  time. 
The  machine  must  be  so  designed  and  so  operated  that  a  close  approxi- 
mation to  the  results  possible  with  full-sized  flotation  machinery  will 
be  obtained.  In  a  mill-plant  it  is  a  matter  of  some  difficulty  to  control 
conditions  through  a  wide  range  of  such  variables  as  temperature, 
acidity,  quantity  of  oil,  percentage  of  solids  in  pulp,  fineness  of  grind- 
ing, etc.,  and  as  the  proper  treatment  of  a  given  ore  can  be  ascertained 
only  through  testing  it  first,  a  critique  of  the  testing  methods  in  use 
is  in  order. 

Many  people  have  had  the  experience  of  reading  the  available 
literature  on  flotation  testing  and  of  failing  to  get  satisfactory  results 
when  the  described  testing  was  attempted.  To  actually  witness  some 
good  test-work  and  learn  thereby  the  appearance  of  froth,  the  exact 
manipulation  of  the  machine  and  froth,  goes  far  toward  bringing  the 
beginner  to  a  point  where  he  can  test  efficiently.  None  of  the  literature 
mentions  the  fact  that  it  is  difficult  to  get  a  high  percentage  of  extrac- 
tion and  a  high  grade  of  flotation  concentrate  at  the  same  time.  The 
beginner  often  strives  after  both  of  these  things  in  a  single  test, 


76  FLOTATION 

whereas  he  should  determine  how  each  can  be  attained  before  he  at- 
tempts to  obtain  both  simultaneously.  Furthermore,  it  is  difficult  to 
manipulate  a  small  machine  to  give  as  good  results  as  a  large  one,  until 
after  considerable  practice.  So  the  small  machine  is  generally  pessi- 
mistic, compared  with  the  large  one.  It  is  practically  essential  for  the 
beginner  to  weigh  and  assay  all  of  his  products  in  order  to  see  if  the 
extraction  and  the  grade  of  concentrate  are  satisfactory,  where  an  ex- 
perienced manipulator  can  often  tell  by  aid  of  past  experience  and 
the  use  of  a  glass  or  microscope  whether  he  is  getting  good  results 
or  not. 

With  these  points  in  view,  we  shall  describe  first  the  satisfactory 
machines  and  their  operation.  Then  we  shall  give  a  more  general 
exposition  on  what  variablts  to  study  and  what  points  to  observe. 

Flotation  test-apparatus  must  necessarily  be  classified  in  the  same 
way  as  large-scale  machines,  namely,  as  film-flotation  machines,  acid- 
flotation  machines,  and  froth-machines  of  both  pneumatic  and  me- 
chanically agitated  types.  Film-flotation,  as  exemplified  in  the  Mac- 
quisten1  and  in  the  Wood  machines,  does  not  seem  to  have  the  same 
wide  application  as  does  froth-flotation;  hence  little  need  be  said 
about  them. 

The  Wood  machine  can  be  built  in  miniature  and  for  several  years 
a  small  machine  of  the  type  sketched  has  been  used  in  the  plant  of  the 
Wood  ore-testing  works  at  Denver.2  This  small  machine  was  about  two 
feet  long  and  one  foot  wide.  The  method  of  operation  is  the  same  as 
that  of  the  full-sized  machine.  (See  Fig.  1.) 

As  neither  of  these  machines  has  been  much  used  in  practice,  they 
are  merely  mentioned  for  the  sake  of  completeness.  Hoover3  has 
recommended  a  test  on  a  vanning-plaque,  so  that  the  sulphides  will 
float  off  onto  the  surface  of  the  water,  but  we  consider  this  test  of 
practically  no  value.  Hoover,  however,  acknowledges  that  it  is  merely 
a  test  illustrative  of  the  film  processes. 

In  testing  ores  for  the  Potter  or  the  Delprat  processes,  Hoover's 
text  is  again  the  source  of  information.  A  200-c.c.  beaker  is  used  with 
100  c.c.  of  3%  H2S04  and  brought  to  nearly  boiling  temperature.  The 
ore  when  introduced  into  this  yields  a  froth  composed  of  sulphides 
supported  by  bubbles  of  C02.  In  case  the  ore  is  deficient  in  carbonate, 
an  addition  of  as  much  as  3%  of  calcite  or  siderite  is  made.  The  froth 
is  skimmed  with  a  spoon  as  fast  as  it  forms.  We  have  noticed  that  a 


iM.  &  S.  P.,  Vol.  XCVI,  page  414  (1908). 

2H.  E.  Wood.    Trans.  A.  I.  M.  E.,  Vol.  XLIV,  pp.  684-701  (1912). 

«T.  J.  Hoover.    'Concentrating  Ores  by  Flotation/  1st  edition,  page  77. 


TESTING   ORES 


77 


great  deal  of  mineral  is  often  lifted  partly  but  never  reaches  the  sur- 
face. Consequently  extractions  are  low,  although  the  grade  of  con- 
centrate obtained  is  often  very  good.  For  practical  purposes,  however, 


FlG.    1.      THE    WOOD    MACHINE 

the  test  is  not  of  much  value.  A  better  test-machine  is  the  small  unit 
shown  in  Fig.  2.  The  acid  should  be  allowed  to  run  down  through  a 
section  of  garden-hose  to  within  an  inch  of  the  surface  of  the  ore  and 
the  ore  should  be  kept  stirred  with  a  wooden  paddle  so  that  the  bub- 
bles of  C02  generated  by  the  action  of  the  acid  can  lift  the  sulphides 
out  of  the  body  of  the  pulp.  The  froth  formed  should  be  skimmed 
with  the  paddle  as  fast  as  made,  then  filtered,  dried,  weighed,  and 
analyzed.  Not  many  ores  yield  gracefully  to  this  treatment  arid 


78 


FLOTATION 


slimes  give  poor  extractions.  Fines  and  Wilfley-table  middlings  are 
better  adapted,  and  the  presence  of  siderite  in  the  pulp  is  desirable, 
as  it  reacts  slowly  with  dilute  acid.  From  1  to  3%  H,S04  is  best  in 
testing  and  ^  to  1^%  solutions  on  the  large  scale  will  give  about  the 
same  results.  The  temperature  of  the  pulp  should  be  maintained  at 
70°  C.  by  use  of  a  steam  jet.  Five  to  ten  pounds  of  ore  per  test  is 
necessary.  The  extractions  obtained  are  always  lower  than  in  full- 
sized  units.  While  oil  is  not  necessary  in  this  process  it  will  greatly 


Garden  Hose. 

Wooden  Paafcf/e. 


Froth. 


FlG.    2.       A    POTTER-DELPRAT    TEST-MACHINE 


assist  in  the  flotation,  and  the  addition  of  a  small  amount  is  often  of 
much  assistance  in  test-work. 

MECHANICAL  FROTHING  as  developed  by  the  Minerals  Separation 
company  in  England  and  Australia,  and  modified  by  many  others, 
has  been  one  of  the  most  important  methods  of  flotation.  Therefore 
the  laboratory  machinery  that  has  been  developed  is  at  as  high  a  state 
of  perfection  as  any  such  machinery  now  in  use. 

The  Janney  machine  is  probably  the  best  designed  machine  for 
getting  reliable  quantitative  results  on  a  small  quantity  of  ore.  A 
sketch  is  appended  (Fig.  3).  It  can  be  seen  that  the  agitation  com- 
partment is  cylindrical  in  shape  and  that  its  top  is  surrounded  by  a 
froth-box,  which  slopes  into  a  spitzkasten,  where  the  froth  can  be 
skimmed.  The  tailing  sinks  to  a  return-hole  at  the  bottom,  passing 
into  the  agitation-compartment  again.  To  provide  good  agitation,  four 
vertical  baffles  are  attached  to  the  wall  of  the  agitation-compartment, 
against  which  the  pulp  is  swirled  by  the  $wo  impellers.  Lining  the 


TKSTIXG    ORES 


79 


walls  with  expanded  metal  lathing  or  with  a  coarse-mesh  iron  screen 
adds  to  the  thorough  mixing  that  the  pulp  must  receive.  The  two  im- 
pellers are  on  a  common  shafting,  which  enters  the  machine  through  a 
stuffing-box  in  the  bottom  of  the  machine.  The  lower  impeller  with 
four  vertical  vanes  is  submerged;  it  agitates  and  emulsifies  the  pulp 
while  the  upper  impeller,  likewise  with  four  vertical  vanes,  acts  as  a 


Concentrate 
Filter   Cone. 


Step  Bearing.-M- 


k  ---  /0n  --- 


FIG.    3.       THE    JANNEY    TEST-MACHINE 

pump  to  lift  the  pulp  and  beat  air  into  it.  A  pulley  and  belt  connect 
the  shafting  with  a  variable-speed  motor. 

A  dome-shaped  lid  is  used  on  the  machine.  A  small  hole  in  the 
top  of  the  dome  allows  the  introduction  of  oil,  acid,  water,  or  other 
materials  without  the  removal  of  the  lid.  The  lid  is  so  constructed 
that  it  can  be  turned  upside-down  with  the  dome  extending  down  into 
the  froth-box,  and  in  this  position  it  can  act  as  a  funnel.  The  dome 
rests  then  on  the  top  of  the  agitation-compartment  and  no  froth  can 
escape  into  the  froth-box.  This  allows  a  period  of  agitation  of  the 
pulp  before  the  dome-top  is  turned  right-side  up  to  allow  aerated 
pulp  to  overflow  into  the  froth-box  and  down  into  the  spitzkasten, 
where  the  froth  can  be  removed. 

A  discharge-plug  at  the  bottom  of  the  machine  allows  the  flushing 
out  of  tailing  after  the  test  has  been  completed.  So  careful  has  been 


80  FLOTATION 

the  design  of  this  test-machine  that  even  this  discharge-plug  is 
beveled  to  fit  flush  with  the  bottom  of  the  machine  and  thus  afford  no 
dead  space  in  which  the  solids  might  settle. 

The  spitzkasten  is  long  and  narrow,  in  order  to  permit  a  deep 
froth  to  be  formed  and  to  travel  over  as  long  a  space  as  possible, 
before  reaching  the  discharge.  This  tends  to  allow  more  of  the  en- 
trained gangue  to  settle  out  of  the  mineral  froth.  The  sides  of  the 
spitzkasten  are  of  heavy  plate-glass,  each  fastened  to  a  metal-frame  by 
means  of  screws.  The  wrought-iron  shaft  projects  through  a  brass 
stuffing-box  and  is  supported  by  a  ball-bearing  beneath.  All  the  other 
metal  parts  are  of  cast  aluminum. 

The  small  variable-speed  motor  may  be  of  either  D.  C.  or  A.  C. 
type.  F.  G.  Janney  recommends  the  use  of  a  General  Electric,  shunt- 
wound,  direct-current  motor,  for  230  volts,  with  a  rated  speed  of  1700 
r.p.m.  and  J  hp.  The  impeller-shaft  is  to  be  driven  at  1900  r.p.m. 
maximum  speed.  For  speed-control  he  recommends  a  General  Electric 
d'rect-current  field-rheostat,  with  an  ampere  capacity  of  1.25  to  0.063 
at  250  volts. 

In  our  own  laboratory  it  was  desirable  to  use  the  ordinary  city- 
lighting  circuit  of  110  volts,  A.  C.  On  that  account  we  have  found  the 
following  motor  satisfactory:  J-hp.  General  Electric  repulsion  induc- 
tion motor,  single-phase,  60-cycle,  with  full  speed  of  1780  and  carrying 
4.2  amperes  at  110  volts,  or  2.1  amperes  at  220  volts,  depending  upon 
the  voltage  of  the  current  supplied  to  the  machine,  either  voltage  being 
acceptable.  Speed-control  is  obtained  by  the  use  of  an  ordinary  field- 
rheostat  in  series  with  the  motor.  Such  a  motor  has  a  speed  varying 
with  the  load  and  with  the  voltage  applied.  As  the  load  is  practically 
a  constant,  the  speed  will  depend  upon  the  amount  of  resistance  in 
series  with  the  motor.  As  the  majority  of  laboratories  find  a  city 
alternating  current  more  convenient  to  obtain,  such  a  motor  is  recom- 
mended. 

The  operation  of  the  machine  is  as  follows :  It  is  set  up  on  a  bench 
convenient  to  the  sink  and  to  running  water.  The  motor  is  set  up  one 
foot  to  the  rear  with  the  switch  and  rheostat  placed  so  that  they  can 
be  easily  reached  while  standing  in  front  of  the  machine.  A  ^-in. 
round-leather  sewing-machine  belt  is  used  for  drive.  The  bearings 
are  well  oiled,  the  stuffing-box  is  properly  packed,  and  some  attention 
should  be  given  to  it  occasionally  in  order  to  see  that  it  is  kept  screwed 
tight  enough  to  avoid  leakage. 

Enough  clear  water  is  run  into  the  machine  to  barely  show  in  the 
spitzkasten  and  the  motor  is  started  at  its  lowest  speed.  A  500-gm. 


TESTING    ORES  81 

charge  of  ore  ground  to  at  least  48-mesh  is  added  and  the  cover  placed 
on  the  machine  in  its  inverted  position.  This  is  done  to  allow  thorough 
mixing  without  circulation  of  the  pulp.  All  or  part  of  the  oil  and 
other  reagents  are  now  added  and  the  motor  brought  up  to  full  speed 
for  30  seconds.  The  speed  is  again  lowered  to  the  minimum  and  the 
cover  is  turned  over  into  its  upright  position.  The  speed  is  then 
raised  and  water  is  added  through  the  hole  in  the  top  of  the  lid  until 
the  froth  in  the  spitzkasten  is  nearly  at  the  overflow-lip.  The  ulti- 
mate speed  of  the  agitator  will  depend  somewhat  upon  the  character 
of  this  froth,  as  some  oils  will  give  a  deep  persistent  froth,  while  other 
froths  are  thin  and  brittle  and  allow  of  more  water  being  added  to  the 
machine,  as  well  as  more  violent  agitation  in  order  to  beat  more  air 
into  the  pulp.  The  froth  may  either  be  allowed  to  flow  out  of  the 
spitzkasten  of  its  own  weight  or  skimmed  with  a  small  wooden  paddle. 
It  is  a  good  idea  to  wet  the  glass  sides  of  the  'spitz'  with  water  while 
the  froth  is  rising,  so  that  none  of  the  froth  will  stick  to  the  glass. 

The  duration  of  the  test  is  about  five  minutes  with  an  ore  that 
floats  easily,  while  other  ores  will  require  a  considerably  longer  time 
to  allow  the  entrained  gangue  to  settle  out  of  the  froth  before  it  is 
discharged  from  the  machine.  In  such  cases  it  is  best  to  hold  back  the 
froth  until  its  appearance  shows  it  to  be  fairly  clean.  Beginners  are 
likely  to  dilute  their  froth  with  too  much  gangue.  In  a  large-sized 
machine  the  froth  can  travel  over  from  four  to  eight  feet  of  spitz- 
kasten before  it  is  discharged,  while  in  this  test-machine  it  only  has  a 
travel  of  about  10  inches.  Consequently,  the  small  machine  is  liable 
to  yield  concentrate  of  too  low  a  tenor.  The  same  applies  to  most  other 
machines  for  making  tests  on  flotation. 

The  concentrate  may  be  caught  in  a  pan  or  on  a  filter.  After  the 
test  the  machine  is  brought  back  to  low  speed  and  the  tailing-plug 
removed,  so  that  the  tailing  can  be  caught  in  a  pan  or  bucket,  or  run 
to  waste. 

If  it  is  so  desired,  this  rough  concentrate  can  be  put  back  into  the 
machine  and  treated  in  the  same  way  as  the  original  sample,  or  the 
concentrates  from  several  tests  combined  to  give  enough  material  for 
re-treatment.  If  this  is  done  three  products  are  made,  namely : 

A  'rougher'  tailing,  to  waste. 

A  clean  concentrate,  for  shipment. 

A  'cleaner'  tailing  or  middling,  which  in  actual  practice  is  re- 
turned to  the  head  machine. 

"When  these  conditions  are  observed  results  only  slightly  lower 
than  those  possible  with  a  big  machine  can  be  obtained.  A  test  can 


82 


FLOTATION 


be  run  in  from  5  to  30  minutes  in  such  a  machine  with  500  grammes  of 
ore  in  anything  from  a  3 : 1  to  a  5 : 1  pulp.  The  glass  sides  of  the 
spitzkasten  allow  close  observation  of.  the  condition  of  the  froth,  and 
this  is  a  great  advantage  to  the  beginner.  The  small  amount  of  ore 
necessary  for  a  test  is  a  matter  of  considerable  convenience,  as  fine 
grinding  of  the  ore  in  the  laboratory  is  often  irksome.  The  aluminum 
casting  is  little  corroded  by  either  acid  or  alkaline  electrolytes.  The 
return  of  pulp  from  the  'spitz'  to  the  agitating-compartment  allows 
the  material  to  be  treated  until  all  mineral  has  been  removed  without 
stopping  the  machine,  so  that  a  single  treatment  yields  a  clean  tail- 
ing. However,  a  second  treatment  of  this  'rougher-froth'  is  some- 
times necessary  in  order  to  get  a  high-grade  concentrate.  Clean  tail- 
ings generally  mean  only  medium-grade  concentrates  due  to  entram- 
ment  of  gangue,  in  the  removal  of  all  the  mineral. 

The  stuffing-box  in  the  bottom  will  probably  leak  if  not  watched. 
However,  this  driving  of  the  impellers  from  below,  instead  of  from 
above,  leaves  the  top  of  the  machine  free  for  the  operator  and  is  more 
convenient  in  every  way.  This  is  of  importance  in  a  laboratory- 
machine,  and  will  excuse  the  use  of  a  stuffing-box.  In  large-scale 
machines  a  stuffing-box  underneath  would  not  be  tolerated,  and  the 
drive  should  be  from  above.  We  would  also  suggest  a  sheet-lead 
construction  as  being  more  easily  built.  A  |-inch  sheet-lead  is  suffi- 
ciently rigid  to  stand  up  well,  while  it  is  ductile  enough  to  be  worked 
readily  into  the  desired  shape.  The  joints  are  easily  burned,  and  it 
is  acid-proof. 

THE  HOOVER  MACHINE,  Fig.  4,  was  designed  "after  a  test-machine 
described  in  the  second  edition  of  Hoover's  book,  being  copied  from 


FIG.    4.       ORIGINAL   FORM    OF    HOOVER   TEST-MACHCNE 

one  of  Lyster's  patents,  and  has  been  much  copied  by  people  wishing 
to  make  flotation  tests.  An  improvement  over  this  construction  was 
published  by  Ralph  Smith4  recently,  and  a  modified  form  of  the  samQ 


.  &  M.  J.,  Vol.  C,  page  395  (1915). 


TESTING    OKES 


FlG.    5.      THE  CASE   FLOTATION    MACHINE 


84  FLOTATION 

is  shown  in  Fig.  5,  which  is  that  sold  by  the  Denver  Fire  Clay  'Co. 
under  the  name  of  the  Case  machine,  for  $75.  Either  a  variable-speed 
motor  is  belted  to  the  pulley  that  drives  the  stirring  mechanism,  or  a 
pair  of  cone-pulleys  on  a  constant-speed  motor  is  used.  A  less  original 
machine  but  a  fairly  useful  one  is  that  described  in  the  Mining  & 
Scientific  Press  of  April  15,  1916,  which  is  said  to  be  used  at  the 
Suan  Concession,  Korea.  All  of  the  dimensions  are  given  in  the 
drawing  (Fig.  6)  so  that  it  can  easily  be  built.  Its  capacity  is  said 
to  be  100  Ib.  per  hour  and  its  total  cost,  including  the  motor,  is  under 
$50.  It  is  used  for  checking  small-scale  tests  and  occasionally  for 
separating  chalcopyrite  from  scheelite  in  small  lots.  This  construction 
has  been  popular  because  it  can  be  made  of  wood,  at  small  expense. 
Tke  Janney  machine  will  cost  about  $125,  while  the  Hoover  machine 
can  be  built  for  a  small  fraction  of  that  amount.  Mr.  Hoover 's 
original  drawing  does  not  show  the  spitzkasten  drawn  to  a  point,  as 
only  the  front  side  was  beveled.  Our  sketch  shows  both  sides  beveled. 
This  is  desirable,  as  it  eliminates  space  in  which  fine  sand  can  settle, 
and  tends  to  minimize  the  amount  of  pulp  lying  inactive  in  the  spitz- 
kasten. In  the  agitation-compartment  the  pulp  is  swirled  into  the 
corners,  where  it  is  well  mixed  with  air ;  hence  the  baffles  sketched  in 
the  Janney  machine  are  unnecessary.  One  objection,  however,  is  that 
unless  the  agitation-compartment  is  very  tall  the  pulp  being  swirled 
into  the  corners  has  a  tendency  to  splash  out,  and  a  lid  similar  to  the 
one  on  the  Janney  machine  is  desirable.  However,  it  is  difficult  to. 
attach  one  because  the  stirrer-shafting  is  in  the  way.  The  operation 
of  this  machine  is  practically  the  same  as  that  of  the  Janney,  except 
that  without  glass  sides  on  the  spitzkasten  it  is  hard  to  get  as  clean  a 
froth. 

One  very  simple  and  inexpensive  machine  of  recent  development 
is  the  McPherson,  shown  in  F'ig.  7.  As  can  be  seen,  it  is  of  the  ordinary 
agitating-box  and  spitzkasten  type.  A  disc-drive  from  a  counter- 
shaft, driven  at  constant  speed,  and  capable  of  adjustment  such  that 
the  driving  disc  may  be  moved  in  or  out  from  the  centre  of  the  fric- 
tion-disc, allows  of  variation  in  speed.  Such  a  machine  does  not  call 
for  a  variable-speed  motor  and  this  is  its  main  claim  to  novelty.  The 
body  of  the  machine  is  of  rather  light  construction  being  made  of 
sheet-metal  and  painted  with  acid-proof  paint.  It  is  sold  for  $35  by 
the  Calkins  Company  of  Los  Angeles. 

A  most  interesting  test-machine  is  that  of  Roy  &  Titcomb,  of 
Nogales,  Arizona,  which  is  run  by  hand-power  by  means  of  gears  and  a 
balance-wheel.  This  machine  is  shown  in  Fig.  8.  The  impeller  shaft 


TESTING    ORES 


85 


•J%/*etiim,ft9f»  fbrc/eaning, 
to  be  filfvct  wfth  ap/ug 


L  cad  or^  Copper  Pipe 

£  "/ns/cte  a/tarn.  — 


fmpe/ffr,  periphfrical  speed 
/500tv/800 


FlG.    6.      FLOTATION   MACHINE   USED   AT   THE   SUAN   CONCESSION,    KOREA 


86 


FLOTATION 


is  suspended  on  ball-bearings  and  the -cells  are  cast  in  one  piece.  The 
PV  ssibility  of  taking  such  a  hand-driven  machine  into  remote  localities 
for  test-work  is  immediately  suggested.  It  costs  $85.  . 

THE  SLIDE  MACHINE,  as  shown  in  Fig.  9  and  10,  was  designed  by 
Hoover  and  perfected  by  many  others.  In  recent  practice  it  is  motor- 
driven.  A  number  of  these  machines  were  given  by  James  M.  Hyde  to 
various  universities  in  this  country.  Many  people  favor  this  apparatus 


FIG.  7.    THE  M'PHERSON  FLOTATION  MACHINE 

for  the  reason  that  they  have  had  little  opportunity  to  use  any  other 
design.  In  this  machine  the  agitator  is  driven  from  below  through  a 
stuffing-box,  as  in  the  Janney,  with  the  consequent  freedom  of  the  top 
of  the  machine  for  the  convenience  of  the  operator.  The  top  half  of 
the  machine  is  so  constructed  that  it  can  be  slid  to  one  side,  cutting  off 
the  froth  formed  in  the  agitation  from  the  gangue,  which  is  allowed  to 
settle.  The  operation  consists  in  agitating  with  oil  and  other  reagents, 
then  a  period  of  quiet  during  which  the  frpth  collects  at  the  top  while 


TESTING    OKKS 


87 


the  gangue  sinks.  Two  windows  in  the  side  enable  the  observer  to  see 
when  the  gangue  has  subsided  sufficiently  to  allow  the  top  half  to  be 
slid  along  the  rubber  gasket,  cutting  off  the  froth  from  the  remainder 
of  the  pulp.  The  time  necessary  for  the  settling  of  the  gangue  is 
sufficient  for  much  of  the  gangue  to  separate  from  the  froth,  leaving 


FlG.    8.      ROY   &    TITCOMB   TEST-MACHINE 


only  clean  sulphides  in  the  froth.  This  element  of  the  machine  has 
made  it  of  some  value  in  testing  flotation-oils,  but  in  a  weak  froth 
much  of  the  sulphide  mineral  also  settles  out  and  is  lost,  so  that  the 
test  results  with  this  machine  often  show  unnecessarily  low  extractions 
and  a  high  grade  of  concentrate.  On  the  other  hand,  when  conditions 
are  adjusted  to  give  a  froth  persistent  enough  to  hold  all  the  sulphide 


88  FLOTATION 

mineral,  considerable  gangue  is  entrained  in  the  stilt'  froth.  Further, 
after  skimming  one  froth  we  find  it  necessary  to  add  more  water  and 
start  the  machine  again  to  make  more  froth.  It  is  hard  to  make  the 
slide  machine  give  a  high  extraction  with  only  one  agitation.  The 
intermittent  character  of  such  work  and  the  time  necessary  to  wait 
while  settling  are  disadvantages  that  make  the  Janney  or  the  Hoover 
machines  of  greater  utility,  in  our  opinion.  The  parts  are  of  cast 


FIG.   9.      THE  SLIDE  MACHINE 

aluminum  with  a  rubber  gasket  between.     A  charge  of  500  to  1000 
grammes  of  ore  is  used. 

One  other  test-machine,  designed  more  recently,  is  that  of  Kraut  & 
Kollberg,  often  referred  to  as  the  K.  &  K.  It  is  a  reproduction  of  the 
larger  machine  of  the  same  make  (shown  on  another  page)  although  it 
does  not  do  the  large  machine  full  justice  in  the  test-work  done.  It 
consists  of  a  cylindrical  rotating  drum  covered  with  longitudinal 
riffles  contained  within  a  cylindrical  casing  placed  on  one  side  of  a 
spitzkasten,  into  which  the  agitated  pulp  is  thrown  by  the  motion  of 
the  rotating  drum.  It  is  adapted  to  a  charge  of  about  2  lb.  or  1000 
gm.  of  ore.  It  is  opened  by  loosening  the  hinged  top  which  is  held 
by  thumb-screws.  A  great  deal  of  time  is  necessary  in  cleaning  out 
this  machine  after  a  test.  The  tailing  can  be  drained  out  by  pulling 
a  stopper  in  the  bottom.  Oil  and  other  reagents  are  introduced  during 
a  test  through  a  small  hole  in  the  front.  Sand  will  tend  to  accumulate, 
during  a  test,  on  the  bottom  of  the  machine.  Fast  and  loose  pulleys  are 
provided  and  the  speed  recommended  is  400  r.p.m.  The  machine  is 
sold  by  the  Braun  Corporation  of  Los  Angeles  for  $75, 


TESTING    ORES 


89 


SEPARATORY  FUNNELS.  During  the  past  year  an  article  on  practice 
in  Mexico5  mentioned  the  fact  that  much  of  the  preliminary  testing 
on  the  ore  was  done  in  separatory  funnels,  in  which  the  charges  of 
pulp,  oil,  etc.,  were  shaken,  after  which  the  cock  at  the  bottom  of  the 
funnel  was  opened  and  the  tailing  run  into  a  second  separatory  funnel 
for  further  flotation  tests,  the  cock  being  closed  in  time  to  catch  the 
froth.  The  versatility  of  experiment  shown  by  the  use  of  such 


LONGITUDINAL   SECTION. 

FIG.    10.      THE   SLIDE    MACHINE 

apparatus  (Fig.  11)  is  commendable.  Obviously,  this  arrangement  is 
open  to  the  same  objections  as  is  the  slide  machine,  except  that  sepa- 
ratory funnels  are  simple  and  inexpensive. 

ELMORE  MACHINE.  As  far  as  we  know,  no  small  test-machine  for 
the  Elmore  process  has  come  into  common  use  on  account  of  the  fact 
that  the  pulp  must  be  lifted  through  a  tube  corresponding  in  length 
to  the  column  of  water  equivalent  to  barometric  pressure.  This  makes 
an  awkward  laboratory  machine.  Mr.  Hoover  (2nd  edition,  page  98), 
describes  "illustrative"  experiments  with  the  pulp  in  a  bottle  con- 
nected with  a  water-pump  for  producing  a  vacuum,  but  no  quantita- 
tive method  of  this  kind  has  been  developed. 


•M.  &  S.  P.,  Vol.  CXI,  page  122  (July  24,  1915). 


90  FLOTATION 

Other  miscellaneous  frothing  tests  are  in  the  literature  but  most 
of  them  are  merely  "illustrative."  Putting  a  charge  into  a  soda- 
water  siphon,  pumping  in  air  to  dissolve  the  water,  and  then  releasing 
the  charge  into  a  beaker  gives  nice-looking  froth.  In  some  of  the 
lawsuits  square  glass  candy- jars  (Fig.  12)  with  a  motor-driven  im- 
peller have  been  used  to  show  flotation  phenomena  in  court.  In  a 
recent  U.  S.  Patent  (No.  1,155,836)  taken  out  by  T.  M.  Owen,  one  of 


FIG.    11.      SEP AR \TORY    FUNNEL 

the  engineers  of  the  Minerals  Separation,  Ltd.,  is  a  sketch  of  a  simple 
test-machine  made  of  an  ordinary  2^-litre  acid-bottle.  (See  Fig.  13.) 
This  corresponds  to  the  .sub-aeration  type  of  machine  and  is  recom- 
mended by  Mr.  Owen  for  test-work  when  such  a  type  of  machine  seems 
necessary,  as  in  differential  flotation.  Air  is  led  into  the  pulp  through 
the  stopper  in  the  bottom  and  beaten  into  the  pulp  by  the  impeller. 
The  four  large  baffles  above  the  impeller  prevent  the  swirling  of  the 
pulp  from  rising  through  them,  so  that  there  is  a  quiet  zone  in  the 
top  of  the  machine  where  the  froth  can  collect.  One  great  beauty  of 
such  a  machine  is  that  any  froth  formed  will  rise  immediately  to  the 


TESTING    ORES 


91 


AIK  CONNECTION 


PULLEY^, 


ROTATING 

HOLLOW 

TO  ADMIT  AlR 


AIR  HOLES 

FIG.    12.       THE   SQUARE  GLASS   JAB   MACHINE 


92 


FLOTATION 


discharge.    However,  we  believe  that  the  Janney  and  Hoover  machines 
are  the  most  useful  of  the  mechanically-agitated  type. 

PNEUMATIC  FLOTATION.  Among  the  different  pneumatic  machines, 
as  far  as  we  are  acquainted,  the  Callow  test-machine  is  the  only  one  of 
laboratory  size  that  has  been  much  developed.  It  is  merely  the  com- 


Pulley. 


1 

_ 

-.--  — 

J 

..-/C/pycc    l/jr 

-<- 

.^-4  Baffles. 
x-  Impeller. 

L  cz 

i 

h4 

Wooden  Cork. 
—  Pipe  Nipple. 
v^  Check Valve. 

/-^/r  Inlet, 


FlG.     13.       OWEN    TEST-MACHINE 


mercial  Callow  machine  reduced  in  size.  ( See  Fig.  14. )  Later  develop- 
ment in  the  laboratory  of  the  General  Engineering  Co.,  in  Salt  Lake 
City,  has  resulted  in  the  reproduction  of  the  whole  plant  in  miniature, 
with  Pachuca  mixer,  roughing-cell.  cleaning-cell,  vacuum-filter,  and 
sand-pump  to  return  middling  to  the  Pachuca  mixer.  As  seen  in  the 
drawing,  the  pulp  is  mixed  well  in  a  Paohuca  tank  of  small  size,  over- 


TESTING    ORES 


93 


flowing  into  the  rougher  flotation-cell.  The  tailing  from  this  rougher 
goes  to  a  sand-pump  and  is  returned  to  the  Pachuca.  The  froth  is 
treated  in  a  second  and  smaller  pneumatic-flotation  unit,  giving  a  con- 
centrate that  overflows  into  an  ordinary  laboratory  vacuum-filter 
actuated  by  a  water  or  aspirating  pump.  The  tailing  from  the 
'cleaner-cell'  consists  of  a  middling  that  likewise  .flows  to  the  sand- 
pump  and  back  to  the  Pachuca. 

A  novice  will  have  no  small  difficulty  in  operating  such  an  installa- 


Air  Line,  4  /bs.  Pressure 

Pressure  Gauge 
Tailing  from  ftOugher 
and  C/eaner  Celts- 


To  Vacuum 
-*-  Pump.     IfgSaEgS 


FIG.   14.      CALLOW  TEST  SET 


tion,  as  there  are  a  number  of  things  to  be  kept  in  operation  at  the 
same  time.  The  mixture  of  ore,  water,  oil,  and  any  other  reagents  is 
fed  either  into  the  suction  of  the  sand-pump  or  into  the  top  of  the 
Pachuca  after  air  has  been  started  into  the  various  machines.  The 
overflow  from  the  Pachuca  into  the  rougher-cell  accumulates  until  a 
nice  froth  is  coming  up  and  nearly  overflowing.  Then  the  tailing- 
discharge  valve  on  the  rougher  is  gradually  opened  and  froth  al- 
lowed to  overflow  from  the  cell  into  the  'cleaner '-cell.  It  is  best  to 
get  most  of  the  charge  circulating  before  much  concentrate-froth  is 
allowed  to  overflow,  the  overflow^  of  froth  being  controlled  by  the 
main  air-valves  leading  to  each  unit.  After  the  valves  into  the  in- 
dividual wind-boxes  beneath  the  machine  have  been  once  adjusted  they 
should  never  be  disturbed,  and  all  control  of  air  supplied  should  be 
at  the  valves  in  the  main  pipes.  When  everything  is  going  well,  the 
air-pressure  in  the  cleaner  can  be  increased  until  concentrate-froth  is 
overflowing  into  the  vacuum-filter.  A  wooden  paddle  to  stir  any 
settled  material  in  the  flotation  cells  is  of  value,  as  well  as  a  small  jet 


94  FLOTATION 

of  water  from  a  rubber  hose  for  washing  concentrate  along  the  froth- 
launders  and  for  beating  down  froth  when  occasional  too-violent  rushes 
of  froth  from  the  cells  take  place.  After  a  test  is  complete  the  pulp 
should  be  drained  completely  from  all  parts  of  the  machine  while  the 
air  is  still  blowing,  so  that  solids  will  not  settle  in  passages  or  clog  the 
canvas  blanket  in  the  cells.  Only  practice  will  allow  anyone  to  get 
reliable  results  with  this  machine.  A  watch-glass  for  catching  and 
panning  occasional  samples  of  froth  is  another  necessary  auxiliary  to 
this  equipment.  The  cost  of  installing  such  a  set  of  apparatus  is  from 
$100  to  $150.  At  least  1000  grammes  of  ore  is  required  for  a  test  and 
about  30  minutes  to  1  hour  is  spent.  It  can  be  seen  that  nothing  but 
a  finished  concentrate  and  a  tailing  are  obtained.  The  machine  is  said 
to  give  results  closely  paralleling  those  obtained  with  larger-scale 
apparatus.  A  source  of  supply  of  compressed  air  at  3  to  5  Ib.  per  sq. 
in.  is  necessary  and  the  main  valves  on  the  air-pipe  leading  to  each 
machine  should  be  of  some  type  of  needle-valve  in  order  to  ensure 
exact  control. 

LABORATORY  MANIPULATIONS.  Turning  from  the  description  of  the 
machines  used  to  the  operations  on  the  ore  before  and  after  the  flota- 
tion operation,  we  have  in  general  the  problems  of  crushing  the  ore 
and  of  drying  the  froth-concentrate. 

As  a  rule  laboratory  machinery  for  the  pulverization  of  ore  is  of 
the  dry-grinding  type,  with  the  exception  of  small  ball-mills  that  can 
crush  from  1  to  100  Ib.  charges  in  the  wet.  Consequently,  most  people 
start  with  weighed  charges  of  finely-ground  dry  ore,  a  known  quantity 
of  water,  of  oil,  and  of  acid  or  alkali.  Our  experience  has  been  that 
most  dry-ground  ore  must  be  treated  in  an  acidified  pulp  to  get  good 
flotation.  Doubtless  the  surfaces  of  sulphide  particles  become  some- 
what oxidized  in,  or  shortly  after,  dry  grinding  and  the  function  of 
the  acid  would  be  to  clean  the  slightly  oxidized  surfaces.  Wet  grind- 
ing usually  does  not  call  for  so  much  acid.  One  interesting  experience 
is  that  of  L.  B.  Pringle,  working  on  ores  from  south-east  Missouri. 
He  found  that  drying  of  a  sample  of  mill-slime  before  floating  in  a 
laboratory  machine  gave  a  much  higher  tailing  and  a  lower-grade  lead 
concentrate.  On  that  account  the  laboratory  samples  were  kept  under 
water  and  the  proper  weight  of  pulp  was  obtained  for  each  test  by  the 
use  of  a  graduate  and  a  hydrometer,  always  taking  enough  of  the  pulp 
to  get  500  grammes  of  solid.  Sulphuric  acid  did  not  seem  to  rectify 
the  oxidation  effect  obtained  in  drying  because  calcium  and  magnesium 
carbonates  tended  to  float  with  the  concentrate  in  the  acid  pulp. 

In  nearly  all  laboratory  work  finer  griwdincr  than  is  used  in  practice 


TESTING    ORES  95 

seems  to  be  necessary.  This  may  possibly  be  due  to  the  smaller 
amounts  of  froth  that  are  formed.  Such  small  quantities  of  froth 
cannot  form  layers  as  deep  as  those  made  in  the  large  machines.  If  a 
big  particle  of  sulphide  can  be  entrained  with  a  number  of  smaller 
particles,  it  can  be  floated,  but  with  a  thin  froth  the  chance  of  such 
entrainment  would  seem  to  be  less.  Some  experimenters  have  in- 
formed us  that  they  were  able  to  float  even  as  large  as  30-mesh  ma 
terial,  but  our  own  experience  is  that  60-mesh  material  is  often  hard 
to  float  with  any  chance  of  getting  a  high  extraction,  while  the  opera- 
tion is  performed  with  much  more  ease  and  expedition  when  the  ore 
is  crushed  somewhat  finer. 

Wet  grinding  is  more  desirable,  as  it  parallels  conditions  in  prac- 
tice, where  most  of  the  finer  grinding  of  ore  is  in  Chilean,  tube,  and 
other  mills.  However,  wet  grinding  is  harder  to  manipulate  in  a  small 
laboratory  and  requires  more  time.  The  dry  weight  of  the  feed  to  the 
flotation  machine  must  be  known;  hence  a  weighed  charge  of  dry  ore 
crushed  to  about  10-mesh  can  be  introduced  into  a  porcelain  or  iron 
pebble-mill  for  grinding  and  ground  for  the  length  of  time  found  neces- 
sary to  reduce  the  pulp  to  sufficient  fineness — 15  minutes  to  24  hours. 
The  charge  can  then  be  poured  and  washed  through  a  coarse  screen 
(to  retain  the  pebbles)  into  a  bucket  and  thence  into  the  flotation 
machine.  The  oxidation  of  sulphide  surfaces  is  thus  avoided,  but 
separate  grinding  of  each  charge,  in  order  to  know  its  exact  weight,  is 
rather  tedious  and  requires  a  number  of  small  mills  if  many  tests  are 
being  run,  on  account  of  slow  speed  in  grinding.  A  mill  with  iron 
balls  rather  than  pebbles  is  of  greater  service.  It  is  possible  to  intro- 
duce the  flotation-oil  before  grinding,  to  be  sure  .that  it  will  be  thor- 
oughly mixed.  For  thick  viscous  oils  this  is  highly  beneficial,  as  a  ball- 
mill  gives  about  the  best  conditions  for  agitation  and  mixing.  Usually 
1  to  2  Ib.  charges  are  used  and  a  small  laboratory  mill  of  the  Abbe  type 
serves  well,  although  a  good  mill  can  be  made  with  a  10-in.  length 
of  8-in.  iron  pipe  and  two  heavy  iron  caps  for  the  same. 

Practice  in  our  laboratory  has  been  standardized  to  a  laboratory- 
gyratory  breaker  crushing  to  10-mesh,  splitting  into  weighed  samples 
kept  in  paper  bags  and  reduced  to  smaller  size  by  either  wet  or  dry 
grinding  as  occasion  demands. 

A  short-stemmed  tin  funnel  about  6  inches  in  diameter  with  a  one- 
inch  opening  is  found  to  be  about  the  most  convenient  means  of  pour- 
ing a  charge  of  ore  into  a  laboratory  flotation-machine. 

The  measuring  and  testing  of  flotation-oils  in  the  laboratory  has 
been  very  inexact  in  many  instances  witnessed  by  us.  It  is  common 


96  FLOTATION 

practice  to  count  the  number  of  drops  of  oil  falling-  from  a 
small  piece  of  glass  tubing.  We  are  using-  a  Mohr  pipette  of 
1  c.c.  total  capacity  for  measurement  of  the  amount  of  oil 
used  in  each  test.  Such  a  pipette  is  shown  in  full  size  in 
Fig.  15.  It  will  be  seen  that  this  pipette  allows  measure- 
ment of  the  oil  to  the  nearest  0.01  c.c.,  which  is  as  close  as 
will  ever  be  desired.  If  the  density  of  the  oil  is  known,  the 
volume  as  measured  by  this  method  is  quickly  converted 
into  the  weight  of  oil  used. 

The  testing  of  oil  samples  for  flotative  power  is  a  matter 
that  needs  standardizing.  It  is  desirable  to  classify  oils 
according  to  flotative  power,  but  just  how  to  do  this  is  not 
exactly  clear.  A  unit  of  'flotativeness'  might  be  established 
and  each  oil  referred  to  that  unit  in  terms  of  percentage. 
But  it  has  to  be  remembered  that  the  best  oil  for  one  ore 
may  not  prove  to  be  the  best  oil  for  another,  although  two 
such  series  of  oils  might  roughly  parallel  each  other.  For 
any  given  ore,  it  would  be  permissible  to  make  such  a 
measurement  on  a  series  of  oils  and  group  them  according 
to  some  definite  standard.  A  standard  oil  might  be  chosen 
and  the  value  of  a  second  oil  expressed  in  percentages  of 
the  flotative  power  of  the  first  as  determined  by  using  equal 
quantities  of  the  two  oils  in  tests  on  an  ore  under  identical 
conditions.  This  test  could  not  be  fair  for  the  reason  that 
different  amounts  of  two  different  oils  are  necessary  to  ac- 
complish the  same  results.  Further,  the  conditions  of  acidity 
or  alkalinity  might  favor  one  oil  and  handicap  another.  If 
we  measured  the  amount  of  oil  necessary  to  give  a  fixed 
percentage  of  recovery  the  first  of  the  above  objections  would 
be  satisfied  but  conditions  of  acidity  or  alkalinity  could  make 
the  test  unfair  for  some  oils.  Hence  the  dilemma  as  to  a  stand- 
ardized test  of  a  flotation-oil. 

No  single  test  could  definitely  place  an  oil  in  any  scheme 
of  classification  and  nothing  can  be  done  but  run  a  series  of 

tests  using  varying  amounts  of  the  oil  to  be  tested  and  with  varying 

acidity  or  alkalinity.     The  temperature  of  the  pulp  must  be  kept 

constant  although  it  has  a  minor  effect. 

Coutts  gives  about  the  only  directions  on  oil-testing  that  are  to  be 

found  in  the  literature  of  the  subject.6     He  states  rightly  that  the 


«J.  Coutts.    E.  &  M.  J.,  Vol.  XCIX,  page  1079  (1915). 


TESTING    ORES  9? 

first  thing  to  do  with  an  oil  is  to  measure  its  density,  for  future  calcu- 
lations, as  it  will  be  measured  by  volume  in  the  laboratory  and  must 
later  be  reduced  to  weights.  He  recommends  the  use  of  a  burette  for 
measuring  the  oil,  but  we  favor  the  Mohr  pipette  mentioned  above. 
He  chooses  a  standard  ore  on  which  all  tests  are  to  be  run  and  classifies 
three  different  kinds  of  standard  tests:  (1)  for  mixed  sulphides,  (2) 
differential  separation,  and  (3)  flotation  of  copper  and  iron  sulphides. 
He  states  that  oils  high  in  phlanderene  have  proved  best  for  differen- 
tial separation  of  zinc-lead  sulphide  ores.  While  this  is  helpful,  he 
does  not  state  just  how  the  oils  are  to  be  classified  after  the  tests  have 
been  made. 

Much  work  with  oils  is  needed  in  order  to  determine  if  there  are 


PIG.   16.      CALLOW   QUALITATIVE  TESTE3 

any  definite  constituents  in  oils  that  give  them  flotative  power.  Re- 
search is  also  needed  in  the  preparation  of  oils  from  the  wood,  coal,  and 
mineral  oils  in  such  a  manner  that  they  will  have  maximum  efficiency 
in  flotation.  Work  on  this  subject  has  been  initiated  in  our  own 
laboratory  and  it  is  known  that  several  of  the  larger  companies  have 
employed  oil-chemists  to  look  into  such  problems.  We  understand 
that  most  excellent  work  is  being  done  on  methods  of  modifying  and 
reconstructing  oils  that  can  be  had  cheaply.  By  this  we  mean  more 
than  mere  mixing  of  a  good  flotation-oil  with  a  cheaper  non-selective 
oil.  Sulphonating  the  oils,  dissolving  them  in  acids,  dissolving  modify- 
ing substances  in  the  oils,  etc.,  are  some  of  the  ideas  being  tested  with 
varying  success.  It  is  on  account  of  all  this  oil-testing  that  consider- 
able progress  has  been  made  in  flotation  during  the  past  few  years,  so 
that  now  most  of  the  larger  companies  are  using  cheaper  oils  than  they 
were  formerly. 

When  starting  to  work  with  a  new  ore,  there  is  needed  a  rapid 
qualitative  method  of  choosing  an  oil  that  seems  well  adapted  to  the 
flotation  of  the  ore  in  question.  Such  a  scheme  is  in  use  in  the  labora- 
tory of  the  General  Engineering  Company  in  Salt  Lake  City.  Their 


98 


FLOTATION 


qualitative  tester  is  designed  to  test  oils  for  use  in  the  Callow  pneu- 
matic flotation  cell  and  consists  of  a  glass  tube  of  about  two  inches 
diameter  and  two  feet  long.  (Fig.  16.)  This  can  be  set  on  end  and 
closed  at  the  bottom  with  a  one-hole  rubber  stopper  through  which 
passes  a  glass  tube  into  a  small  canvas  bag.  The  small  bubbles  of  air 
coming  through  the  canvas  are  similar  to  those  used  in  large-scale  ma- 
chines and  can  be  observed  through  the  glass  walls  of  the  tube.  With 
some  pulp  in  the  tube,  oils,  acids,  salts,  etc.,  may  be  added  in  very  short 


Callow  Tube  - 


Bolt-head 
sofdered  on  —' 


Stiffening  Washer.--'     / 
Tight  Rubber  Ring  '' 


-Cloth  Cover, 
bound  on 


-Holes  in  Me*al 
Wind  Box 

--Rubber  Cork 


>  Air  Inlet 


Wind  Box.-. 


Air  Inlet--. 


'••Plaster  of  Paris  setting, when 
Rubber  Plug  is  not  available 

FlG.  17.       METHOD  OF  PLACING  POROUS  BOTTOM  IN  OIL-TESTER 

tests  until  the  proper  appearance  is  obtained.  An  overflow  lip  is  pro- 
vided in  case  it  is  desired  to  examine  the  mineral  in  the  froth.  A 
slight  adjustment  of  the  air  will  provide  an  ample  overflow  of  froth. 
Two  alternative  methods  of  making  the  bottom  of  such  a  cylinder,  as 
published  by  Alfred  T.  Fry,  of  Broken  Hill,  in  the  Mining  and 
Scientific  Press  of  February  3,  1917,  are  shown  in  Fig.  17. 

DISPOSAL  OF  THE  FROTH.  The  handling  of  the  flotation  froth  in 
the  laboratory  finds  difficulties  which  are  reflected  in  practice.  It  is 
often  very  slow  to  settle  and  filters  with  difficulty.  A  vacuum-filter, 
connected  with  a  laboratory  aspirating  pump,  is  a  very  convenient 


TESTING    ORES  99 

method  of  getting  the  concentrate  out  of  the  froth.  A  large  porcelain 
Buechner  funnel  fitted  into  a  filtering  flask,  as 'shown  in  Fig.  3,  is 
used  at  present  in  our  laboratory.  A  copper  vacuum-filter  of  much 
the  same  type,  provided  with  a  porous  false  bottom  of  acid-proof 
wire-cloth,  resting  on  a  punched  plate,  is  shown  in  Fig.  14  of  the 
Callow  test  set.  Filter-papers  can  be  laid  over  the  bottom  of  either 
of  these  funnels  to  collect  the  concentrates  and  the  vacuum  beneath 
sucks  out  the  water  and  oil  of  the  froth.  Such  a  filter  can  be  placed 
under  the  froth -discharge  of  a  flotation  machine  so  that  a  fairly  dry 
cake  of  concentrate  is  ready  for  further  drying  at  the  end  of  the  flota- 
tion test.  By  loosening  the  outer  rim  of  the  filter-paper  and  then 
turning  the  funnel  upside  down  over  a  pan,  the  filter-paper  with  the 
concentrate  can  be  dropped  into  the  drying-pan  by  gently  blowing  into 
the  stem  of  the  funnel.  This  is  set  aside  in  a  warm  place  to  dry  and 
later  weighed  against  a  filter-paper  tare. 

If  it  is  desired,  the  froth  can  be  collected  in  a  glass  beaker  or 
other  vessel  and  allowed  to  stanch  over-night.  A  layer  of  clear  water 
can  then  be  siphoned  off  and  the  thick  pulp  remaining  filtered  or 
dried  direct.  In  some  laboratories  the  froth  is  dumped  onto  a  shallow 
pan  on  a  hot  plate  and  the  water  evaporated.  Occasionally  such  a 
sample  of  froth  will  be  left  too  long,  and  will  be  ignited  and  roasted. 
We  once  used  a  numbered  set  of  shallow  pans  for  such  evaporations 
but  prefer  filtering  before  drying  the  precipitate.  A  numbered  tag  is 
now  put  in  each  pan  along  with  the  cake. 

The  products  coming  from  the  flotation  machine  should  be  watched 
closely  and  occasionally  panned  or  examined  with  the  microscope  to 
see  what  kind  of  work  is  being  done.  This  is  fairly  easy  to  determine 
as  the  sulphides  are  most  of  them  distinguished  easily  from  the  gangue 
under  the  miscroscope,  and  likewise  gangue  particles  in  the  froth  con- 
centrate can  often  be  distinguished.  A  microscope  is  a  most  useful 
adjunct  in  a  flotation  laboratory  or  mill. 

GENERAL  CONSIDERATIONS.  We  have  mentioned  at  various  places 
the  relation  of  the  laboratory  tests  to  the  large-scale  operations  and 
now  repeat  that  in  almost  every  instance  the  laboratory  results  are 
somewhat  pessimistic  as  compared  to  large-scale  work.  The  reasons  are 
made  apparent  by  the  smallness  of  the  machine  and  the  shallower  layer 
of  froth  often  formed  under  these  conditions.  Moreover,  laboratory 
operations  seem  to  call  for  greater  amounts  of  oil,  acid,  etc.,  than  do 
the  large-scale  operations. 

Only  one  of  the  above  machines  is  adapted  to  'roughing'  and 
'cleaning'  operations  in  a  single  test.  Present-day  practice  tends 


100  FLOTATION 

toward  re-treatment  of  at  least  part  of  the  froth  in  order  to  make 
cleaner  and  higher-grade  concentrates.  Consequently,  it  may  be 
desirable  to  collect  enough  froth  from  a  series  of  tests  to  be  re-treated 
in  a  'cleaning'  test.  Of  course,  this  is  provided  for  in  the  Callow  test 
set,  where  only  'cleaned'  concentrate  is  discharged  from  the  machine. 
It  is  further  found  desirable  to  weigh  and  analyze  some  of  the  suc- 
cessive fractions  of  the  froth  being  discharged  from  a  flotation  ma- 
chine, as  the  tailing  becomes  leaner,  and  determine  at  what  point  it 
may  be  desirable  to  re-treat  such  froth. 

Many  reports  of  flotation  test-work  with  mechanical-agitation  ma- 
chines give  the  speed  of  the  rotation  of  the  agitating-blades.  We 
have  found  that  it  was  possible  to  get  much  the  same  work  done  with 
quite  a  variation  of  speeds,  the  only  effect  being  to  lengthen  or  shorten 
the  time  of  treatment.  We  feel  that  the  importance  of  this  matter  has 
been  much  exaggerated.  Some  means  of  speed-control  is  necessary 
and  the  speed  can  be  adjusted  in  each  case  until  the  froth  presents 
the  proper  appearance  as  to  depth,  size  of  bubbles,  color,  etc.  Speed- 
ing toward  the  end  of  a  test  in  order  to  give  a  deeper  froth  with  a 
faint  line  of  concentrate  on  the  very  top  is  often  advisable.  We  recom- 
mend adjusting  the  speed  in  each  test  to  suit  the  other  conditions, 
rather  than  running  a  series  of  tests  with  different  speeds.  Only  in 
the  slide  machine,  where  operation  of  the  impeller  must  be  suspended 
in  order  to  allow  froth  to  collect,  is  the  speed  of  much  importance. 
Here  we  recommend  agitation  for  a  definite  length  of  time,  and  then  a 
period  of  settling.  The  effect  of  variation  of  speed  during  a  definite 
length  of  time  may  be  a  considerable  variation  in  the  amount  of  froth 
collected  during  the  quiet  period.  Hence  we  are  prejudiced  against 
the  use  of  the  slide  machine  except  for  oil-testing. 

When  a  good  set  of  conditions  has  been  found  for  the  flotation 
treatment  of  an  ore,  it  is  best  to  recover  the  water  from  each  test  to 
see  what  effect  a  closed  circuit  of  the  mill-water  will  have.  Some  oil 
and  chemicals  are  thus  recovered,  cutting  down  the  amounts  necessary 
for  operation.  In  fact,  a  carboy  or  two  of  the  water  to  be  used  in  the 
large  mill  should  be  used  to  make  certain  that  no  deleterious  con- 
tamination will  ensue  from  this  source.  Under  these  conditions  filtra- 
tion of  the  concentrate  and  tailing  for  recovery  of  the  water  is  neces- 
sary. Such  conditions  are  provided  for  in  the  Callow  apparatus, 
above  described,  and  can  be  applied  easily  to  any  of  the  other  machines. 

Oil  samples  for  test  purposes  can  be  obtained  from  the  various 
wood-distilling  companies  now  advertising  in  the  technical  press,  from 
gas  companies  and  from  petroleum-refining  companies. 


TESTING    ORES  101 

Tn  attacking:  refractory  ores,  there  are  a  number  of  ingenious 
things  that  can  be  done  to  the  pulp  both  in  and  out  of  the  machine. 
The  trouble  may  be  due  to  deleterious  substances,  which  sometimes 
can  be  washed  out,  rendered  harmless  by  boiling,  or  by  acidifying,  or 
by  making  alkaline  with  lime  before  entering  the  machine.  Occasion- 
ally, the  ore  will  not  work  well  under  ordinary  conditions  but  will 
yield  beautifully  after  finer  grinding.  Sometimes  extra  reagents 
are  necessary,  such  as  powdered  charcoal,  modified  oil,  argol,  soap, 
calcium  sulphate,  alum,  etc.  A  rational  method  of  devising  the  proper 
tests  in  such  cases  must  be  based  on  some  theory  of  flotation.  Colloid 
chemistry  is  a  branch  of  knowledge  that  we  believe  to  be  very  necessary 
for  such  work,  as  it  has  facilitated  a  more  intelligent  control  of  our 
tests  and  has  given  wonderful  results  in  a  number  of  instances. 

Finally,  it  is  well  to  be  prodigal  in  the  amount  of  analytical  work 
connected  with  flotation  testing  in  order  to  discover  interesting  differ- 
ences in  gangue-constituents  carried  into  the  concentrate,  as  well  as  to 
find  the  best  conditions  for  leaving  out  some  gangue  constituent  that 
is  less  desirable  than  the  rest.  If  an  experimenter  does  his  own 
analytical  work  he  can  be  expected  to  spend  three-fourths  of  his  time 
analyzing  what  has  been  done  during  the  other  fourth. 


102  FLOTATION 


DIFFERENTIAL  FLOTATION 

BY  0.  C.  RALSTON 
(Written  especially  for  this  volume) 

INTRODUCTION.  Many  names  are  used  to  express  the  fundamental 
idea  conveyed  by  the  above  title.  'Preferential'  is  used  more  particu- 
larly to  designate  the  process  claimed  in  patents  issued  to  E.  J.  Hor- 
wood  of  Australia.  'Differential'  implies  that  one  mineral  is  being 
floated  to  a  greater  degree  than  another  flotative  mineral  also  pres- 
ent. Moreover,  it  is  a  broader  term  than  'preferential'  because  the 
latter  is  coming  to  mean  the  process,  patented  by  the  man  who  used  it 
first,  equivalent  to  fractional  roasting'and  flotation.  'Differential'  has 
found  acceptance  in  England  and  in  Australia  but  it  has  not  yet  been 
adopted  in  the  United  States. 

For  the  benefit  of  those  who  have  not  read  my  earlier  compilation 
misnamed  'Preferential  Flotation,'*  it  may  be  well  to  abstract  a  por- 
tion and  to  state  that  differential  flotation  is  now  obtainable  in  three 
ways: 

I.  By  fractional  roasting  and  flotation. 

II.  By  the  use  of  certain  dissolved  substances  in  the  pulp. 

III.  By  close  control  of  the  physical  conditions  regulating  flota- 
tion. 

I.  FRACTIONAL  ROASTING.  H.  A.  "Wentworth,  in  U.  S.  patent  No. 
938,732,  of  1909,  claimed  the  fractional  roasting  of  "ore  mixtures 
containing  several -sulphides, "  so  that  one  mineral  would  be  deadened 
while  the  others  would  float.  He  seems  to  have  meant  film-flotation. 

A.  S.  Ramage,  in  U.  S.  patent  No.  949,002  of  1910,  stated  that  the 
"principle  of  my  process  is  founded  on  the  combination  of  fractional 
roasting  with  chemical  floating ; "  in  other  words,  he  had  particularly 
in  mind  the  warm-acid  methods  of  DeBavay,  Potter,  and  Delprat. 

E.  J.  Horwood,  in  U.  S.  patent  No.  1,020,353  of  1912  and  No. 
1,108,440  of  1914,  claims  "preferential- flotation,"  which  depends  on 
deadening  the  surfaces  of  such  minerals  as  galena  and  pyrite  by  a 
short  flash-roast,  while  sphalerite  and  chalcopyrite  are  unaffected  and 
can  be  later  removed  by  flotation.  This  processf  has  been  employed 
on  the  Broken  Hill  mines  of  the  Zinc  Corporation  and  the  flotation 


*M.  &  S.  P.,  June  26,  1915.    Also  'The  Flotation  Process,'  by  T.  A.  Rickard, 
p.  71. 

tThe  operation  of  this  process  is  well  described  by  Allan  D.  Rain  in  a 
separate  paper  elsewhere  in  this  volume. 


DIFFERENTIAL    FLOTATION  103 

used  has  been  the  modern  air-frothing  method  of  the  Minerals  Separa- 
tion company. 

Fractional  roasting  and  flotation  are  said  to  be  in  use  in  the  North 
Star  mill  of  the  Federal  Mining  &  Smelting  Co.,  near  Hailey,  Idaho. 
The  most  serious  objection  to  it  is  the  large  amount  of  sulphuric  acid 
necessary  in  order  to  obtain  good  flotation  of  the  zinc  sulphide  after 
the  roasting.  The  iron  sulphides  are  effectively  deadened. 

In  the  mill  of  the  Progress  Mining  &  Milling  Co.,  near  Robinson, 
Colorado,  a  complex  zinc-iron-lead  ore  is  receiving  table-treatment  to 
make  a  good  lead  concentrate  and  a  zinc-iron  middling.  This  middling 
is  roasted,  ground,  and  treated  in  a  mechanical  agitator  for  flotation 
of  the  zinc. 

In  U.  S.  patents  1,197,589  and  1,197,590  of  September  12,  1916, 
Raymond  F.  Bacon  calls  attention  to  the  fact  that  in  such  frac- 
tional-roasting processes  part  of  the  minerals  that  it  is  desired  to  have 
deadened  will  not  be  oxidized  and  part  of  those  that  are  not  wanted 
to  oxidize  are  nevertheless  oxidized.  Besides,  in  some  ores  the  sul- 
phides are  so  intimately  mixed  that  a  clean  separation  is  impossible  by 
any  crushing  process.  He  inclines  toward  more  complete  oxidation 
of  the  ore,  followed  by  sulphidizing  with  a  soluble  sulphide,  or  even 
getting  one  of  the  constituents  into  solution  and  then  sulphidizing. 
Thus,  for  pyritic  ores  containing  some  copper,  the  treatment  recom- 
mended is  to  roast  long  enough  to  completely  decompose  the  iron  sul- 
phides, although  part  of  the  chalcopyrite  will  resist  roasting.  Dur- 
ing the  roasting  part  of  the  copper  minerals  will  also  be  roasted  and 
lost  if  treated  directly  by  most  of  the  previously  mentioned  methods 
of  fractional  roasting  and  flotation.  Bacon  treats  the  fractionally 
roasted  ores  with  enough  sulphuric  acid  to  get  the  copper  into  solution 
and  then  adds  hydrogen  sulphide  to  precipitate  it  as  sulphide.  The 
flotation  treatment  that  follows  will  then  recover  both  the  natural  and 
the  artificial  sulphides  of  copper. 

In  the  case  of  copper-zinc  sulphides  the  same  idea  can  be  applied.  A 
complete  roasting  .of  the  ore  is  necessary,  and  then  copper  and  zinc 
are  taken  into  solution  by  sulphuric  or  other  acid.  The  application  of 
hydrogen  sulphide  to  the  pulp  containing  this  solution  will  precipitate 
only  copper  sulphide.  After  flotation  of  the  copper  sulphide  tho.  pulp 
is  neutralized  and  an  alkaline  sulphide  is  added  to  precipitate  zinc  sul- 
phide, which  is  then  likewise  floated  to  remove  it  from  the  gangue.  In 
commenting  on  this  process,  I  would  say  that  in  the  first  place  the  com- 
plete roasting  of  zinc  sulphide  is  a  difficult  and  expensive  operation. 
Secondly,  there  would  almost  certainly  be  some  iron  dissolved  from  the 


104  FLOTATION 

ore  and  it  would  accompany  the  zinc,  being  precipitated  as  iron  sul- 
phide with  the  zinc  sulphide.  This  is  undesirable  from  the  standpoint 
of  the  zinc  smelter.  Moreover,  the  flotation  of  copper  sulphide  in  the 
presence  of  large  amounts  of  zinc  and  iron  sulphides  in  solution  pre- 
sents considerable  difficulty.  Since  Dr.  Bacon  also  claims  the  applica- 
tion of  this  method  directly  to  oxidized  ores,  as  well  as  to  the  above- 
mentioned  suiplude  ores,  and  as  oxidized  ores  nearly  always  contain 
considerable  amounts  of  acid-soluble  iron  compounds,  I  am  inclined  to 
believe  that  he  has  obtained  a  'paper  patent.' 

Numerous  other  separations  of  this  kind  are  claimed  in  his  patent. 
Nickel-copper  ores  and  lead-silver-zinc  ores  are  mentioned.  The  use 
of  sulphurous  acid  in  place  of  sulphuric  acid  is  also  specified. 

While  the  underlying  chemical  ideas  described  in  this  patent  are 
excellent,  I  feel  justified  in  stating  that  the  practical  details  of  flota- 
tion in  such  solutions,  the  cost  of  the  large  amount  of  chemicals  re- 
quired in  many  cases,  and  the  difficulties  of  roasting  in  other  cases,  are 
enough  to  make  the  process  too  costly. 

I  have  recently  unearthed  a  British  patent  containing  a  somewhat 
different  idea.  It  was  granted  to  Sulman  &  Picard,  consulting  chemists 
to  Minerals  Separation.  Ltd.,  and  is  numbered  8650  of  1910.  While 
its  claims  are  more  broad  than  here  indicated,  the  particular  appli- 
cation is  to  roast  mixed  sulphides  to  oxides;  then  to  treat  the  roasted 
ore  at  about  600°  C.  with  carbon  or  a  reducing  gas.  Only  the  easily 
reducible  metals,  such  as  lead  and  copper,  will  be  reduced  to  metallic 
form,  while  zinc  and  iron  are  not  affected.  Hence,  theoretically,  at 
least,  it  should  be  possible  to  obtain  a  separation.  Whether  the  process 
works  satisfactorily  I  do  not  know.  It  should  be  a  good  method  for 
recovering  lead  and  copper  left  in  a  zinc  concentrate,  but  it  would,  of 
course,  be  undesirable  where  the  zinc  concentrate  contains  much  iron. 
However,  to  roast  completely,  to  an  oxide,  an  ore  containing  zinc  sul- 
phide, is  a  long  and  costly  operation  and  it  has  yet  to  be  proved  that 
the  subsequent  reduction  gives  a  product  capable  of  economical  separa- 
tion by  flotation.  It  is  now  generally  known  that  metallic  copper,  in 
a  finely  divided  condition,  can  be  floated  satisfactorily,  and  it  is  pos- 
sible that  the  same  can  be  done  with  freshly  reduced  lead,  but  there  is 
no  certainty  that  the  ore  will  be  in  such  a  physical  condition  after  re- 
duction that  these  reduced  metals  can  be  separated  from  the  other 
metallic  oxides  in  the  ore. 

II.  USE  OF  DISSOLVED  SUBSTANCES.  The  first  mention  of  the  use 
of  dissolved  substances  in  obtaining  differential  flotation  was  con- 
tained in  British  patent  23,870  of  1910,  granted  to  Henry  Lavers,  E. 


DIFFERENTIAL    FLOTATION  105 

H.  Nutter,  and  Minerals  Separation.  This  was  probably  the  first  truly 
differential  method  on  record.  Most  of  the  patent  is  devoted  to  claims 
of  differential  flotation  by  varying  the  physical  conditions,  such  as 
dilution  and  aeration,  but  there  is  also  mention  of  the  fact  that  differ- 
ential flotation  can  be  obtained  by  adding  soluble  substances  to  the 
water  of  the  pulp.  This  patent  was  also  granted  in  the  United  States, 
No.  1,067,485  of  1913.  As  no  specific  mention  is  made  of  the  dissolved 
substances  that  effected  good  differential  separation  and  as  the  num- 
ber of  dissolved  substances  that  might  possibly  be  used  is  infinite,  it  is 
hard  to  see  why  such  a  patent  should  have  been  granted. 

CHROMATES.  The  next  important  process  of  this  kind  was  that  of 
H.  H.  Greenway  and  A.  H.  P.  Lowry,  British  patent  11,471  of  1913 
(also  U.  S.  1,102,738  of  1914).  This  consists  of  treating  the  ore  with 
a  solution  of  a  bi-chromate  either  before  or  during  flotation.  Such 
minerals  as  galena  and  pyrite  will  be  wetted  by  this  solution  and  min- 
erals like  molybdenite,  sphalerite,  and  chalcopyrite  can  then  be 
floated  differentially  from  their  mixtures  with  either  pyrite  or  galena. 
The  inventors  of  the  process  soon  learned  that  much  better  work 
could  be  done  by  performing  the  flotation  in  an  alkaline  pulp,  in  the 
presence  of  a  bi-chromate,  and  the  result  of  their  discovery  was  em- 
bodied in  British  patent  16,302  of  1913  and  U.  S.  1,142,820  of  1915. 
For  example,  the  pulp  may  advantageously  contain  an  amount  of  so- 
dium carbonate  equivalent  to  1%  by  weight  on  the  ore.  This  combina- 
tion of  a  chromium  salt  and  alkalinity  in  the  pulp  is  claimed  to  give 
particularly  good  results.  Two  examples  of  its  success  are  mentioned 
in  the  patent  specifications. 

The  first  example  is  that  of  an  ore  containing  9.0%  lead,  28.2% 
zinc,  and  14.2%  iron,  which  was  finely  crushed  and  then  subjected  to 
froth-flotation  in  apparatus  of  well-known  type  by  being  agitated  vig- 
orously with  four  times  its  weight  of  water  at  130°  F.  containing  in  so- 
lution sodium  carbonate  amounting  to  22  Ib.  per  ton  and  sodium  bi- 
chromate amounting  to  about  6  Ib.  per  ton  of  ore.  The  oil  used  was 
a  mixture  of  half  a  pound  of  eucalyptus  oil  with  an  equal  weight  of 
kerosene  per  ton  of  ore.  The  flotation  product  contained  50.1%  Zn, 
4.25%  Pb,  and  8.3%  Fe,  while  the  bulk  of  the  iron  and  lead  was  left 
in  the  residue.  Of  course,  the  reaction  of  sodium  carbonate  on  sodium 
bi-chromate  would  be  such  as  to  produce  sodium  chromate,  for  bi- 
chromates do  not  exist  in  alkaline  solution.  It  is  also  to  be  noticed  that 
the  percentage  of  zinc  remaining  in  the  lead  and  iron  product  is  not 
specified.  My  own  experience  in  the  laboratory  with  this  process  is 
that  it  is  difficult  to  make  as  clean  a  separation  as  might  be  desired 


106  FLOTATION 

unless  the  pulp  is  heated.  In  the  cold  it  does  not  seem  to  work  well 
unless  a  long  treatment  with  the  chromate  solution  is  given  and  even 
then  low  extractions  of  zinc  are  the  general  rule. 

The  second  example  is  of  slime  containing  11.6%  lead  and  13.4% 
zinc.  This  was  introduced  into  an  agitator  with  four  tons  of  water 
per  ton  of  ore  and  24  Ib.  of  sodium  carbonate.  One  pound  of  eucalyp- 
tus oil  per  ton  of  ore  was  used  and  the  flotation  was  done  at  130°F. 
with  the  formation  of  a  floating  concentrate  containing  22.2%  Pb  arid 
27.4%  Zn.  The  concentrate  was  then  subjected  to  differential  bi- 
chromate flotation  in  pulp  containing  24  Ib.  sodium  carbonate  and  6 
Ib.  sodium  bi-chromate.  The  oil  consisted  of  0.75  Ib.  kerosene  and 
0.25  Ib.  eucalyptus  oil  per  ton  of  ore.  The  flotation  contained  48.6% 
Zn  and  7.5%  Pb,  while  the  residue  contained  8.9%  Zn  and  55.9% 
Pb.  This  is  particularly  interesting  as  it  shows  that,  even  after  oil- 
ing and  flotation,  the  minerals  can  be  so  modified  by  an  addition-agent 
that  only  one  will  float.  Further,  the  separation  is  commonly  regarded 
as  good.  It  is  a  matter  of  considerable  ease,  however,  to  juggle  tests 
so  that  they  look  as  well  as  these  in  comparison  with  the  test  in  which 
only  sodium  carbonate  was  used  in  the  pulp.  I  have  noticed  that  in  the 
flotation  of  such  a  mixed  ore  in  an  alkaline  pulp  it  is  not  unusual  for 
the  galena  to  float  first,  particularly  if  a  small  amount  of  oil  is  used, 
and  by  further  addition  of  oil  the  zinc  can  be  floated,  so  that  the 
composite  concentrate  is  much  like  the  first  above  mentioned.  For  pur- 
poses of  obtaining  a  patent,  however,  such  an  experiment  is  excellent. 

NEUTRAL  OR  ALKALINE  CHLORIDES  OR  SULPHATES.  F.  J.  Lyster 
was  the  next  successful  inventor  to  patent  a  differential  flotation  pro- 
cess of  this  kind,  which  was  assigned  to  Minerals  Separation.  His  pro- 
cess was  first  tsied  by  the  Zinc  Corporation  at  Broken  Hill.  It  pur- 
ports to  be  only  an  improvement  on  the  fundamental  differential  pat- 
ent 23,870  of  1910,  mentioned  above,  and  is  British  patent  11,939  of 
1913 ;  also  U.  S.  1,203,372  of  October  31,  1916.  This  process  applies 
ostensibly  to  the  separation  of  galena  and  sphalerite.  No  heating  of 
the  solution  is  required ;  it  must  contain  a  sulphate,  chloride,  nitrate, 
or  hydrate  of  calcium,  magnesium,  sodium,  or  potassium,  or  a  mixture 
of  them.  It  is  also  possible  to  use  manganese,  zinc,  or  ferrous  sul- 
phates, barium  chloride,  or  the  carbonate  or  bi-carbonates  of  sodium. 
Under  these  conditions  only  the  galena  floats;  the  zinc  sulphide  does 
not  float.  The  zinc  may  be  caused  to  float  later  by  continued  agitation 
«uid  aeration  of  the  pulp,  an  operation  that  is  rather  slow,  or  by  de- 
watering  and  mixing  the  residue  with  fresh  water.  The  effect  of  ex- 
cess of  alkalinity  is  to  cause  poor  differentiation  of  the  galena  from 


DIFFERENTIAL    FLOTATION  107 

the  zinc.  No  fixed  rule  as  to  alkalinity  can  be  given  but  the  water 
should  always  contain  enough  alkalinity  to  react  well  with  methyl 
orange. 

The  water  from  the  mines  at  this  particular  plant  happened  to 
be  of  such  an  analysis  as  to  be  well  adapted  to  this  process.  It  con- 
tained 

Gr.  per  gal. 

Total  soluble  solids 666 

Volatile  organic  matter  57.2 

Silica     2.2 

Calcium   oxide    78.2 

Magnesium  oxide 53.0 

Sulphur  tri-oxide  205.0 

Chlorine    178.0 

Manganese   30.3 

Zinc    5.0 

Alumina   4.0 

Carbon  di-oxide    9.3 

Total 622.2 

Lyster  names  the  different  reagents  that  can  be  used  with  success 
on  the  Broken  Hill  ore  with  which  he  worked  and  which  contained 
11%  zinc  and  13%  lead.  A  few  of  these  mixtures- are 

Gr.  per  gal. 

Calcium  sulphate    160 

Calcium  sulphate    160 

Calcium  hydrate  3.6 

Calcium  chloride 160 

Calcium  hydrate 1.8 

Magnesium   chloride    300 

Sodium  sulphate  800 

Calcium  hydrate  18 

Ferrous  sulphate 300 

Lyster  has  recently  been  granted  four  American  patents  covering 
this  process,  namely  1,203,372  to  1,203,375,  inclusive,  of  October  31, 
1916.  In  these  patents  we  find  the  following  statement:  "I  have 
further  discovered  that  the  residue  obtained  as  before  described,  con- 
taining the  bulk  of  the  zinc  sulphides,  may  be  further  treated  by  flota- 
tion separation  to  produce  a  concentrate  rich  in  zinc  by  first  dewater- 
ing  and  thickening  the  pulp  and  then  submitting  it  to  a  repetition  of 
the  flotation  separation,  using,  however,  sufficient  water  in  lieu  of  the 
solution  previously  described,  or  by  further  continuing  the  process 
herein  described,  after  the  recovery  of  the  lead  sulphide  (galena),  in  a 
separate  dezincing  unit  until  the  zinc  sulphides  (sphalerite)  appear 
upon  the  surface  of  the  solution  and  are  carried  over  into  the  launder. 
In  operation  I  prefer  the  former  to  the  latter  method  for  the  recovery 
of  the  zinc  sulphide.  In  this  way,  a  zinc  concentrate  may  be  obtained 
and  thereby  both  the  lead  sulphide  and  zinc  sulphide  recovered  in  sep- 


108  FLOTATION 

arate  products  by  flotation  separation  without  recourse  to  separation 
by  gravitation  on  tables  or  vanners  as  heretofore." 

ACIDULATED  ALKALINE  CHLORIDES.  These  were  introduced  by  Les- 
lie Bradford,  whose  process  was  taken  up  by  the  Broken  Hill  Proprie- 
tary Co.  It  is  protected  by  British  patent  21,104  of  1913  and  U.  S. 
1,182,290  of  1916.  It  aims  at  the  flotation  of  pyrite  or  of  sphalerite 
in  the  presence  of  galena.  A  solution  of  one  or  more  chlorides  of  the 
alkalies  or  the  alkaline  earths,  preferably  feebly  acidulated,  is  used  as 
a  'wetting  medium'  for  galena.  If  used  neutral  or  akaline  the  con- 
centrate would  contain  too  much  galena  and  \vould  require  re-treat- 
ment. 

A  temperature  of  120-160°F.  is  preferred,  although  some  ores  work 
well  in  the  cold.  Usually,  a  concentrate  produced  in  cold  solution  will 
have  to  be  re-treated.  Bradford  is  unable  to  indicate  the  degree  of 
acidity  required  for  all  ores  but  with  the  ores  on  which  he  has  experi- 
mented he  states  that  if  the  acidity  is  increased  to  1%,  galena  begins  to 
float  again  and  usually  he  has  obtained  good  results  in  solutions  con- 
taining 0.1  to  0.2%  sulphuric  acid.  This  must  be  over  and  above  the 
amount  of  acid  that  is  consumed  by  the  ore.  The  amount  of  salt  can 
be  varied  within  wide  limits  but  a  10%  solution  of  sodium  chloride 
is  a  good  strength  to  use. 

Owing  to  the  fact  that  the  Proprietary  company  is  using  a  modi- 
fication of  the  Potter-Delprat  process,  no  oil  need  be  added  when  treat- 
ing a  crude  ore  containing  calcite  and  siderite.  as  the  gas  generated  by 
the  acid  accomplishes  the  flotation.  However,  the  addition  of  oil  is 
not  objectionable.  After  treatment  in  this  way,  the  pulp  has  to  be 
drained  (or  dewatered)  and  re-floated  in  order  to  obtain  a  concentrate 
carrying  the  galena.  Hence,  it  may  be  preferable  to  make  first  a  mixed 
concentrate  of  the  two  minerals,  galena  and  sphalerite,  and  then  treat 
the  mixed  concentrate  by  this  process.  In  case  the  mixed  concentrate 
has  been  obtained  by  the  use  of  oil,  the  oil  should  be  removed  from  the 
surfaces  o¥  the  particles  by  the  use  of  a  solution  of  sodium  hydrate, 
sodium  carbonate,  or  by  treatment  with  ether. 

Fine  ore  often  tends  to  flocculate  too  fast  and  the  floccules  of  sphal- 
erite entrain  particles  of  galena.  Hence  Bradford  found  it  necessary 
to  use  an  agent  that  would  check  or  slow  down  the  'flotation  tendency.' 
This  idea  was  patented  in  British  19,844  of  1914.  The  best  substances 
to  use  are  sulphites  and  thio-sulphites  of  the  alkaline  metals  or  sul- 
phurous acid,  as  the  latter  is  generated  by  the  action  of  the  acid  in 
the  pulp  on  these  sodium  salts.  Such  a  reagent  is  added  to  the  acidu- 
lated brine  just  before  flotation.  Too  much  of  these  agents  spoils  the 
flotation  but  just  the  right  amount  gives  a  much  cleaner  concentrate. 


DIFFERENTIAL    FLOTATION  109 

British  patent  19,373  of  1914  was  granted  to  the  Minerals  Separa- 
tion and  De  Bavay  companies  for  differential  flotation  applied  to  zinc 
and  lead  s"ulphide  ores,  in  which  the  amount  of  acid  largely  controls  the 
mineral  floated,  although  a  simultaneous  control  of  the  amount  of  oil 
greatly  assists  the  differentiation.  Galena  is  first  floated  by  the  use  of 
a  limited  amount  of  oil  and  too  small  an  amount  of  acid  to  effect  a 
separation  of  both  galena  and  sphalerite  from  the  gangue.  On  the  ad- 
dition of  more  acid  and  more  oil  the  zinc  can  be  separated  by  another 
flotation  treatment. 

When  using  a  circuit-water  already  containing  some  oil,  the  lead 
can  be  floated  without  the  addition  of  oil  and  the  slight  acidity  of  this 
water  does  not  injure  the  flotation.  The  sphalerite  can  then  be  floated 
by  addition  of  oil  and  sulphuric  acid.  If  fresh  water  is  used  a  small 
amount  of  oil  must  be  added  in  order  to  float  the  galena. 

As  an  example  of  the  application  of  this  invention  the  patentees 
cite  the  results  from  treating  the  slime-dump  of  a  Broken  Hill  mill.  It 
contained  10%  lead  and  21%  zinc  and  was  used  in  a  circuit-water 
containing  some  oil  to  which  was  added  22  Ib.  sulphuric  acid  per  ton 
of  ore.  The  galena  concentrate  contained  66%  lead  and  8.8%  zinc 
from  the  first  flotation-cell,  and  the  average  from  all  the  12  cells  of 
the  machine  was  50.5%  lead  and  21.2%  zinc.  The  recovery  of  the  lead 
amounted  to  62.9%. 

Commenting  on  this  process :  it  is  probable  that  any  oil  in  the  re- 
turn-water is  only  the  soluble  portion  of  the  oil  used.  The  fact  that  a 
great  portion  of  the  galena  can  be  floated  by  the  use  of  this  oil  is  in- 
teresting. Sphalerite  is  known  to  require  more  oil  than  galena  and  it 
often  requires  the  presence  of  acid  in  the  solution.  The  large  amount 
of  zinc  in  the  above  concentrate  and  the  low  extraction  of  the  lead  from 
such  a  high-grade  heading  indicates  that  the  process  is  not  a  flattering 
success. 

ACID  AND  REDUCING  AGENT.  Bradford's  work  with  a  'retarder,'  in 
the  process  ascribed  to  him  above,  must  have  brought  about  the  devel- 
opment of  this  present  process.  In  his  first  process  Bradford  floated 
sphalerite  and  pyrite  in  the  presence  of  galena.  In  this  process,  cov- 
ered by  British  21,880,  of  1914,  he  floats  galena  and  pyrite  in  the  pres- 
ence of  sphalerite.  A  slightly  acidulated  mill-water  is  used  and  to  this 
is  added  a  small  amount  of  a  reducing  agent,  like  sulphur  di-oxide,  so- 
dium thio-sulphate,  sodium  sulphite,  or  hydrogen  sulphide.  Bradford 
has  worked  almost  entirely  with  sulphur  di-oxide  or  its  compounds  and 
states  that  he  does  not  know  much  about  the  action  of  other  reducing 
agents.  He  does  not  confine  himself  to  any  particular  proportion  but 


110  FLOTATION 

states  that  he  has  used  from  8  ounces  to  8  pounds  of  reducing  agent 
per  ton  of  ore.  This  renders  the  zinc  sulphide  ' '  temporarily  jmmuiie ' ' 
to  notation. 

Sphalerite  can  be  floated  from  the  residue  by  dewatering  and  re- 
pulping  with  fresh  water,  or  by  the  addition  of  an  oxidizing  agent  or 
by  warming  and  aerating  until  the  sulphur  di-oxide  and  sulphites  are 
oxidized.  An  excess  of  reducing  agent  delays  the  flotation  of  both  ga- 
lena and  sphalerite,  because  the  excess  of  reagent  has  to  be  oxidized  by 
the  aeration  given  the  pulp  in  the  machines  until  the  galena  can  float, 
and  later,  when  further  oxidized,  the  sphalerite  can  float.  Only  enough 
reducer  should  be  added  to  render  the  blende  temporarily  immune. 
Heat  is  not  required  but  assists  greatly,  as  the  oxidation  of  the  reduc- 
ing agent  takes  place  much  faster  and  thereby  the  sphalerite  is  all  the 
sooner  ready  to  float  after  the  galena  and  pyrite  have  been  floated. 
The  apparatus  recommended  by  Bradford  is  a  string  of  centrifugal 
pumps  and  separating-boxes  in  order  that  aeration  can  be  controlled. 
Occasionally,  the  results  are  greatly  enhanced  by  giving  the  pulp  a 
previous  digestion  with  acid  and  the  reducer  before  flotation. 

This  patent  quotes  a  number  of  excellent  examples  of  tests  made 
according  to  the  method  described.  In  one  test  a  500-gm.  lot  of  ore 
was  treated  in  three  litres  of  water  containing  one  gramme  of  sodium 
thio-sulphate  and  enough  sulphuric  acid  to  make  the  water  react  acid, 
and  enough  of  the  regular  frothing-agent.  This  ore  was  a  Broken 
Hill  weathered  dump-slime,  which  was  partly  oxidized.  The  results 

were  as  follows : 

Gm.  Zn,  %  Pb,  %  Ag,  oz. 

Heading    500.0  18.2  15.2  18.3 

Lead  concentrate    79.5  9.6  60.0  69.0 

Zinc   concentrate    166.5  46.4  6.3  15.7 

The  zinc  concentrate  was  obtained  after  the  lead  concentrate  had 
been  taken  off  by  the  addition  of  0.1  gm.  of  potassium  permanganate  to 
oxidize  the  sodium  thio-sulphate. 

In  another  test  with  a  pyritic  blende  ore  the  use  of  sulphurous  acid 
prevented  the  flotation  of  the  blende  while  the  pyrite  was  removed. 
By  thickening  the  pulp  and  discarding  the  sulphurous  acid  solution, 
it  was  possible  to  obtain  a  residue  from  which  the  zinc  could  be  floated 
after  re-pulping  with  fresh  water.  The  table  of  results  is  as  follows : 

Gm.  Zn,  % 

Heading    500  28.3 

Pyritic  concentrate   148  13.4 

Zinc  concentrate    220  51.6 

Tailing 120  3.7 

HYDROCHLORIC   ACID   AND  ZINC   CHLORIDE   are   supposed   to   sink 


DIFFERENTIAL    FLOTATION  111 

galena  and  sphalerite  in  the  presence  of  other  sulphides,  supposedly 
pyrite  and  chalcopy rite,  as  well  as  the  sulphides  of  silver.  This  com- 
bination is  mentioned  in  a  German  patent,  282,131  of  1915,  granted  to 
E.  Languth  of  Neerpelt,  Lembourg,  Belgium.  Nothing  seems  to  be 
known  of  it  beyond  the  statement  that  an  acidified  zinc-chloride  solu- 
tion is  used. 

ALKALINE  SOLUTIONS.  British  patent  9049  of  1914  was  granted  to 
the  Amalgamated  Zinc  (De  Bavay's  Ltd.)  for  the  use  of  alkaline  and 
other  solutions.  Galena  is  wetted  differentially  in  the  presence  of 
sphalerite.  The  patent  recommends  that  a  combined  zinc  and  lead  con- 
centrate be  obtained  by  ordinary  flotation  and  that  the  combined  con- 
centrate of  galena  and  sphalerite  be  re-treated  in  dilute  sodium-carbon- 
ate solution.  The  galena,  wetted  by  the  solution,  sinks  Avhile  a  froth 
rich  in  sphalerite  is  obtained.  It  is  also  recommended  that  if  a  mixed 
concentrate  has  been  obtained  by  the  use  of  an  organic  frothing-agent 
it  should  be  first  treated  with  a  solution  of  hydrogen  sulphide,  sodium 
sulphide,  sodium  sulph-hydrate,  or  other  such  agent  added  to  the 
sodium-carbonate  solutions. 

I  do  not  pretend  to  understand  this  process,  as  all  my  experience 
tends  to  prove  the  contrary :  that  galena  is  more  easily  floated  differen- 
tially in  the  presence  of  sphalerite  in  a  slightly  alkaline  solution.  A 
reference  to  the  paperj  of  Palmer,  Ralston,  and  Allen  on  the  subject  of 
'Some  Miscellaneous  Wood-Oils  for  Flotation'  will  show  that  in  neu- 
tral and  in  alkaline  solutions  most  of  the  oils  tested  gave  differential 
flotation  of  the  galena. 

In  U.  S.  1,203,373  of  October  31,  1916,  Lyster  claims  the  use  of  so- 
lutions containing  alkalies  like  sodium  carbonate  (500  gr.  per  gal. 
water)  or  sodium  bi-carbonate  (600  gr.  per  gal.).  This  patent  ac- 
companies others  claiming  the  use  of 'alkaline  solutions  of  chlorides  or 
sulphates  of  the  alkalies  and  alkaline  earths. 

ALKALINE  SULPHIDES.  British  patent  8746  of  1915,  granted  to 
Minerals  Separation,  covers  the  use  of  sodium  or  similar  sulphides  in 
the  differential  flotation  of  galena  in  the  presence  of  sphalerite.  It 
also  mentions  that  occasionally  the  addition  of  sodium  carbonate  or  of 
a  bi-chromate  is  helpful,  and  that  a  frothing-agent  may  or  may  not  be 
used  and  that  the  solutions  may  be  heated  if  so  desired.  Pyrite  is  also 
said  to  be  floated  differentially  in  the  same  manner,  and  the  sub-aera- 
tion machine  is  recommended.  Beyond  the  mention  of  bare  facts  and 
claims  this  patent  does  not  tell  much ;  no  statement  of  general  princi- 
ples is  given  and  it  is  only  claimed  that  the  "chemicals  are  varied  to 


JBull.  116,  A.  I.  M.  E.,  Aug.  1916,  pp.  1387-1396. 


112  FLOTATION 

suit  the  ore  used,"  with  no  suggestion  as  to  how  this  point  can  be  de- 
termined except  by  * '  experiment. "  It  is  not  even  claimed  that  sodium 
sulphide  has  any  advantage  over  other  alkaline  reagents  and  nothing 
is  said  about  the  fact  that  sodium  sulphide  is  a  reducing  agent.  We 
have  seen  the  use  of  a  reducing  agent,  such  as  the  sulphur  di-oxide,  or 
sodium  sulphite  under  acid  conditions,  patented  by  Bradford.  The 
result  is  the  same  as  in  Bradford's  patent,  the  differential  flotation  of 
galena  and  of  pyrite  in  the  presence  of  sphalerite.  These  patentees 
say: 

1  i  The  process  is  usually  carried  out  in  a  circuit  containing  in  solution 
about  from  0.1%  to  1%  of  a  sulphide  of  an  alkali-metal  or  earth,  such 
as  sodium  sulphide.  The  solution  is  preferably  heated  to  130  to  140 °F. 
and  is  used  with  or  without  a  frothing-agent.  In  certain  cases,  the 
addition  of  a  small  amount  of  about  0.1%  to  0.5%  of  an  alkaline  sub- 
stance, such  as  sodium  carbonate,  may  be  made,  while  in  other  cases 
the  addition  of  a  small  quantity  of  a  bi-chromate  of  an  alkaline  metal, 
such  as  potassium  or  sodium  bi-chromate,  will  be  found  advantageous." 

In  giving  the  details  of  a  number  of  illustrative  tests,  mention  is 
made  of  the  use  of  a  ''sub-aeration  vessel  constructed  of  wood  or  iron" 
but  no  reason  is  given  for  this  stipulation.  Evidently  cast-bronze  or 
aluminum  test-machines  are  taboo. 

MANGANESE  COMPOUNDS.  T.  MacKellar  Owen  has  been  granted 
U.  S.  patent  1,157,176  of  1915  for  the  use  of  alkaline  permanganates  in 
solution  for  accomplishing  differential  flotation  of  various  sulphides. 
"In  the  froth-flotation  treatment  of  mixed  sulphide  ores  containing, 
for  instance,  lead,  copper,  zinc,  and  iron  sulphides,  or  any  two  or  three 
of  these  sulphides,  the  introduction  of  a  small  quantity  of  an  alkaline 
permanganate  into  contact  with  the  slime,  makes  the  flotation  opera- 
tion selective  in  the  case  of  a  large  range  of  representative  slimes.  In 
the  case  of  lead-zinc  slime  the  galena  and  the  blende  are  raised  in  suc- 
cessive order ;  the  galena  is  floated  first,  the  bulk  of  the  silver  if  pres- 
ent, accompanying  the  galena,  and  the  blende  is  subsequently  floated 
from  the  residue  after  acid  has  been  added  to  the  pulp.  If  copper  is 
present  it  usually  comes  up  with  the  lead. 

"The  proportion  of  alkaline  permanganate  required  is  less  than 
the  quantity  that  would  be  necessary  to  change  permanently  the  re- 
ducing character  of  the  mass  of  the  pulp.  Relatively  minute  quanti- 
ties of  free  alkaline  permanganate  will  substantially  affect  the  behav- 
ior of  certain  metallic  sulphides  in  the  flotation  liquor.  *  *  *  The  pre- 
treatment  of  the  water  with  permanganate  to  neutralize  its  reducing 
quality  does  not  produce  the  same  effect  as  having  the  permanganate 


DIKFKKHXTIAL    FLOTATION  113 

present  in  the  pulp  acting  on  the  slimes  during  its 'dissociation. "  It 
is  most  advantageous  to  add  the  permanganate  after  the  slime  has  been 
mixed  with  the  flotation  liquor  as,  otherwise,  it  seems  to  be  wasted  in 
oxidizing  impurities  of  the  water  and  more  quickly  results  in  '  sicken- 
ing' of  the  circuit-liquor.  "Manganese  di-oxide  may  be  used  to  pro- 
cure effects  of  the  same  order  as  alkaline  permanganate. ' '  When  the 
slime  is  of  a  very  reducing  character  and  quickly  decomposes  the  per- 
manganate, it  is  advantageous  to  conduct  the  process  at  a  temperature 
of  approximately  120°  F. 

' '  I  quote  the  case  of  a  weathered  slime  obtained  from  the  treatment 
of  an  ore  obtained  at  Broken  Hill,  N.  S.  W.,  said  slime  containing  ap- 
proximately by  assay  16%  Pb,  13.5%  Zn,  and  17  oz.  Ag  per  ton.  In 
this  treatment,  using  2.5  Ib.  of  potassium  permanganate,  and  3  oz.  eu- 
calyptus oil  per  ton  of  slime,  a  lead  concentrate  was  obtained  contain- 
ing 60.5%  Pb,  54  oz.  Ag,  and  11.8%  Zn,  and  after  adding  15  Ib.  of  sul- 
phuric acid  per  ton  of  original^  slime,  a  zinc  concentrate  containing 
6.2%  Pb,  11.2  oz.  Ag,  and  43.4%  Zn,  leaving  a  residue  containing  2.0% 
Pb,  3  oz.  Ag,  and  1.6%  Zn." 

Owen  describes  the  operating  details  of  his  process  most  frankly. 
The  patent  specification  is  pleasant  to  read  and  I  regret  that  it  is  too 
long  to  be  reproduced  in  full.  If  acid  is  added  in  any  quantity  to  the 
pulp  before  the  lead  is  removed  it  is  impossible  to  get  differential  flo- 
tation, the  lead  and  zinc  sulphides  tending  to  float  together.  In  prac- 
tice Owen  recommends  the  use  of  a  separate  circuit-liquor  containing 
the  manganese  compounds  for  flotation  of  the  lead,  followed  by  de- 
watering  and  re-pulping  with  new  water  for  the  flotation  of  the  zinc. 
This  makes  two  water-storage  tanks  necessary.  Since  the  manganese 
liquor  tends  to  '  sicken '  with  repeated  use,  an  effort  is  made  to  exclude 
contaminations  and  to  introduce  fresh  water  at  this  point  rather  than 
some  other  in  the  system.  Certain  cases,  which  cannot  be  definitely 
defined,  are  found  in  which  the  process  is  commercially  ineffective, 
notably  a  few  cases  of  mixed  iron  and  copper  sulphides.  Only  a  lab- 
oratory test  will  tell.  For  some  slimes  a  preliminary  weathering  of  a 
few  hours  will  greatly  improve  the  results,  and  hence  it  is  advisable 
to  make  experiments  in  the  laboratory  and  take  account  of  this  pos- 
sibility. 

COPPER  OR  MERCURY  OR  THEIR  COMPOUNDS.  British  patent  4974 
of  1915,  to  Minerals  Separation,  covers  the  use  of  metallic  copper  or 
mercury  or  a  compound  or  alloy  of  either  of  the  metals,  in  differential 
separation  of  a  froth  rich  in  zinc  from  a  mixture  of  the  sulphides  of 
lead  and  zinc.  Preferably  the  operation  shall  be  carried  on  in  a  brass 


114  FLOTATION 

or  a  bronze  vessel.  The  invention  is  applicable  to  other  differential 
processes  patented  by  Minerals  Separation  or  its  engineers,  one  ex- 
ample being  the  use  of  chromium  compounds  mentioned  by  Lavers. 
The  copper  metal  can  be  placed  in  the  flotation  machine  in  any  con- 
venient form  such  as  a  sheet-copper  lining,  or  it  may  be  introduced 
with  the  pulp  in  finely  divided  form. 

COPPER  SULPHATE.  The  above  mention  of  the  use  of  metallic  cop- 
per and  copper  compounds  for  differential  flotation  evidently  does  not 
extend  to  the  use  of  soluble  compounds  of  copper.  A  minute  amount 
of  copper  sulphate  in  solution  in  the  mill-water  seems  to  improve  the 
flotation  of  sphalerite.  It  has  been  used  for  this  purpose  in  the  mill 
of  the  Hercules  Mining  Co.,  at  Wallace,  Idaho,  with  only  indifferent 
success,  as  the  object  is  to  drop  some  of  the  pyrite,  which  tends  to  enter 
the  zinc-lead  concentrate.  While  improved  results  are  obtained,  there 
is  still  too  much  iron  in  the  zinc  concentrate. 

CHLORINE  AND  CHLORIDE  OF  LIME.  The  use  of  chlorine  in  an  active 
form,  such  as  is  obtained  by  the  use* of  chloride  of  lime,  seems  to  be 
successful  in  the  treatment  of  products  containing  sphalerite.  In  one 
Canadian  plant  iron  sulphides  are  wetted  by  such  a  solution.  Its  use 
in  the  United  States  has  been  kept  secret.  However,  the  employment 
of  chloride  of  lime  for  flotation  of  galena  in  the  presence  of  sphalerite 
has  been  patented  in  England  (10,478  of  1915,  granted  to  Minerals 
Separation).  Considerable  success  has  been  claimed  for  this  reagent 
and  it  is  hoped  that  information  will  be  forthcoming  in  the  near  future. 
It  may  be  that  chloride  of  lime  has  much  the  same  effect  as  that  ob- 
served in  the  use  of  ordinary  slaked  lime  at  the  Midvale  plant,  Utah, 
where  some  lessees  of  an  old  dump  claim  to  have  prevented  the  flota- 
tion of  iron  by  the  use  of  8  Ib.  of  lime  per  ton  of  ore,  both  sphalerite 
and  galena  being  floated. 

III.  BY  PHYSICAL  CONTROL.  One  of  the  most  important  and  fun- 
damental processes  for  obtaining  differential  flotation  is  disclosed  in 
the  patent  of  E.  H.  Nutter,  Henry  Lavers,  and  Minerals  Separation, 
(U.  S.  patent  1,967,485  of  1913,  and  British  23,870  of  1910.  This 
patent  probably  grew  out  of  observations  on  the  changes  of  froth  pro- 
duced by  varying  physical  conditions  during  flotation.  The  factors 
mentioned  are  "agitation,  aeration,  chemical  constitution  of  the  solu- 
tion employed,  the  degree  of  dilution  of  the  pulp,  the  temperature,  and 
the  amount  and  character  of  the  f rothing-agents. ' '  The  purpose  seems 
to  be  to  claim  the  idea  of  differential  flotation  in  general  and  the  Min- 
erals Separation  people  evidently  regard  it  as  their  basic  patent  in  this 
line.  In  fact,  most  of  their  subsequent  patents  in  differential  flotation 


DIFFERENTIAL    FLOTATION-  115 

refer  to  this  one,  stating  that  they  are  improvements  and  that  they 
merely  supplement  it. 

The  best  idea  contained  in  the  patent  is  that  occasionally,  by  con- 
trolling physical  conditions  in  just  the  proper  way,  a  froth  containing 
the  minerals  in  certain  ratios  of  size  will  be  obtained,  such  as  a  froth 
containing  most  of  the  copper  sulphides  of  an  ore,  some  fine  sphaler- 
ite, and  some  still  more  finely  divided  gangue.  After  breaking  down 
such  a  froth  the  mixed  froth  can  be  tabled  to  separate  the  various  min- 
erals. After  obtaining  several  different  froths  by  close  attention  to 
any  of  the  above  conditions  it  may  be  possible  to  separate  a  complex  ore 
by  tabling. 

One  of  the  important  physical  conditions  affecting  differential  flo- 
tation seems  to  be  the  variety  and  amount  of  the  oil  or  frothing-agent. 
For  example,  the  process  in  the  patent  of  T.  M.  Owen  (British  16,141 
of  1913)  taken  out  by  Minerals  Separation,  is  designed  to  treat  a 
mixed  zinc-lead  sulphide  ore.  By  the  use  of  a  limited  amount  of  froth- 
ing-agent  in  a  neutral  or  an  alkaline  pulp,  the  galena  can  be  floated  in 
the  presence  of  sphalerite,  and  then  by  the  addition  of  more  oil,  or  by 
more  oil  and  some  acid,  the  sphalerite  can  be  floated.  This  method 
is  in  general  use  throughout  the  North-west,  both  in  the  United  States 
and  in  Canada.  Most  of  the  companies  are  secretive,  however,  and  do 
not  wish  to  allow  publication  of  the  details  of  their  practice.  Suffice 
it  to  say  that  they  are  making  commercial  grades  of  concentrate  but 
that  the  separation  is  never  quite  clean,  and  too  much  zinc  is  left  in 
the  lead  concentrate  and  too  much  lead  in  the  zinc  concentrate.  I  am 
informed  that  this  process  is  at  work  in  the  Hewitt  mill  of  the  Silver- 
ton  Mining  Co.,  at  Silverton,  B.  C.  The  gangue  contains  much  siderite 
and  the  sulphides  are  galena,  sphalerite,  and  silver  sulphides.  The  ore 
is  crushed,  and  the  coarse  galena  tabled.  The  slimed  galena  is  floated 
differentially  in  a  2-cell  M.  S.  machine,  giving  a  concentrate  carrying 
52%  Pb  and  6%  Zn,  while  the  zinc  is  removed  in  a  10-cell  machine  giv- 
ing a  product  carrying  45%  Zn  and  2%  Pb.  The  silver  goes  with  the 
lead,  and  the  extractions  are  said  to  be  85%  of  the  lead,  90%  of  the 
silver,  and  86%  of  the  zinc.  This  is  unusually  good  work. 

Owen  describes  the  treatment  of  slimes  at  the  Broken  Hill  South 
mine.  Ordinary  temperatures  suffice  and  no  acid.  The  lead  is  re- 
moved in  the  first  three  cells  of  an  11-cell  machine  by  the  use  of  one 
ounce  of  eucalyptus  oil  per  ton  of  ore.  This  gives  a  recovery  of  85%  of 
the  lead  in  a  product  containing  60  to  79%  lead.  By  the  addition  of 
more  oil  and  some  sulphuric  acid  70%  of  the  zinc  in  the  ore  can  be  re- 
covered in  a  concentrate  carrying  46%  zinc. 


116  FLOTATION 

V 

Following  Owen's  patent  came  one  taken  out  by  the  Minerals  Sep- 
aration and  De  Bavay  companies,  British  19,374  of  1914.  It  purports 
to  be  an  improvement  over  Lyster's  and  over  the  basic  differential 
patent  23,870  of  1910.  It  is  designed  for  differential  flotation  of 
galena-sphalerite  mixtures.  The  claim  is  that  too  small  amounts  of  oil 
to  float  both  sulphides  will  float  only  the  galena  and  will  give  a  clean 
separation  in  either  neutral  or  alkaline  pulp ;  in  other  words,  flotation 
conditions  are  so  poor  that  only  the  most  easily  floated  mineral,  the 
galena,  is  separated.  The  zinc  in  the  residue  can  be  caused  to  float  by 
the  use  of  more  oil,  with  or  without  the  addition  of  acid.  Aeration  and 
emulsification  are  claimed  to  have  no  effect  on  the  zinc  as  long  as  the 
amount  of  frothing-agent  is  below  the  maximum  required  for  the  lead 
alone.  This  maximum  is  dependent  on  the  condition  of  the  circuit- 
water  and  the  amount  of  dissolved  salts  therein.  While  aeration  is 
said  to  have  little  effect  on  the  zinc,  it  is  to  be  noticed  that  usually  the 
sub-aeration  machine  is  recommended  for  the  flotation  of  the  galena 
in  most  of  these  patents  and  sub-aeration  machines  or  pneumatic 
machines  seem  to  be  best  adapted  to  the  flotation  of  this  mineral. 

This  method  of  flotation  is  in  use  by  the  Sulphide  Corporation  at  its 
Central  mine,  treating  the  slime-tailing  from  the  table-concentration  in 
a  Hebbard  machine.  The  feed  averages  4.2%  lead  and  18%  zinc,  while 
the  lead  concentrate  assays  about  50%  lead.  The  residue  from  the 
first  three  boxes  assays  0.53%  Pb  and  18.5%  Zn.  The  zinc  concentrate 
assays  6%  Pb  and  47.5%  Zn  and  the  tailing  1%  Pb  and  2%  Zn.  The 
recovery  of  lead  is  rather  low. 

It  also  happens  that  during  grinding  one  mineral  will  be  slimed 
while  another  will  not  be  so  thoroughly  ground.  Galena  and  chalco- 
pyrite  are  two  rather  friable  minerals  and  as  galena  usually  accom- 
panies sphalerite,  and  chalcopyrite  usually  accompanies  pyrite,  it  is 
these  two  separations  that  are  of  interest.  As  a  rule  there  is  little 
difficulty  in  getting  a  marked  separation  of  galena  from  sphalerite, 
owing  to  this  fact  alone,  and  likewise  a  separation  of  chalcopyrite  from 
pyrite.  For  the  flotation  of  chalcopyrite  the  plants  of  the  Calaveras 
Copper  Co.,  and  of  the  Mountain  Copper  Co.,  in  California,  as  well  as 
that  of  the  National  Copper  Co.,  in  Idaho,  are  examples. 

The  Minerals  Separation  company  has  taken  out  a  British  patent, 
No.. 5650  of  1915,  that  claims  the  addition  of  finely  divided  carbon  to 
a  pulp  in  order  to  gather  the  galena  in  preference  to  the  sphalerite. 
Any  finely  divided  form  of  carbon,  charcoal,  or  coke  is  said  to  be  satis- 
factory. Preferably  an  alkaline  pulp  should  be  used.  The  finely  di- 
vided carbon  probably  depletes  the  pulp  of  oil  so  that  a  minimum 


DIFFERENTIAL  FLOTATION  117 

amount  of  oil  in  a  slightly  alkaline  pulp  with  excessive  aeration  can  be 
obtained  for  the  differential  flotation  of  the  galena.  This  is  only  a 
guess  on  my  part  but- 1  believe  that  the  absorbent  power  of  the  finely 
divided  carbon  for  oil  is  the  physical  result  involved.  If  the  oil  in  the 
pulp  is  largely  absorbed  by  the  carbon,  only  the  galena  can  get  enough 
oil  to  float.  The  carbon  goes  into  the  froth  and  the  galena  accompanies 
it.  Recent  work  at  the  Magma  Copper  Co.,  in  Arizona,  by  the  General 
Engineering  Co.,  of  Salt  Lake  City,  has  developed  a  fairly  successful 
differential  flotation  of  sphalerite  from  pyrite.  A  small  amount  of  oil, 
together  with  an  alkaline  pulp  and  excessive  aeration  in  Callow  cells, 
aids  the  flotation  of  the  sphalerite.  This  is  improved  by  the  addition 
of  a  small  amount  of  copper  sulphate.  As  little  as  a  tenth  of  a  pound 
of  copper  sulphate  per  ton  of  ore  has  a  noticeable  effect.  A  45%  zinc 
concentrate  and  a  4%  tailing  is  made  from  a  15%  zinc  heading. 

WHAT  KIND  of  differential  flotation  is  most  desirable?  The  usual 
answer  of  the  technical  man  is,  "That  depends  on  circumstances." 
The  circumstances  under  which  a  slime  needing  differential  flotation  is 
generally  produced  are  those  obtaining  in  a  gravity-concentrating  mill. 
It  is  awkward  to  dewater  the  slime  and  give  it  the  fractional  roasting 
demanded  by  some  of  the  patentees.  There  is  no  point  in  dewatering 
the  pulp,  roasting  it,  and  then  putting  it  back  into  the  water  for  fur- 
ther flotation  if  there  is  a  possible  method  of  getting  the  same  results 
without  so  much  trouble.  The  simple  addition  of  a  small  amount  of 
some  chemical  to  the  pulp  or  the  careful  control  of  the  amount  of  oil 
used  offers  a  much  less  expensive  process.  The  dewatering  and  filtra- 
tion of  a  slime  often  costs  20  cents  per  ton  and  a  roast  might  cost  all 
the-  way  from  25c.  to  75c.,  with  attendant  dust-losses.  Against  these 
costs  are  to  be  set  the  amount  of  chemicals  consumed  or  the  extra  power 
expended  when  minute  amounts  of  oil  are  being  used  in  order  to  ob- 
tain flotation  of  only  one  mineral.  However,  where  the  ore  can  be  ob- 
tained in  a  dry  state  with  no  special  effort  it  may  pay  to  use  the 
roasting  method  of  modifying  the  easily  burned  minerals  before  flota- 
tion. Dust  from  an  electro-static  or  an  electro-magnetic  plant,  or  from 
other  dry-concentration  processes,  is  already  in  a  condition  for  such 
treatment.  Moreover,  roasting  is  the  only  sure  way  of  rendering  iron 
pyrite  non-flotative.  In  the  case  of  zinc  ores  this  may  be  well  worth 
while,  as  the  smelters  do  not  like  to  take  much  iron  in  the  concentrate. 
The  wonderful  resistance  of  zinc  sulphide  to  roasting  grieves  the  zinc 
smelter-men  but  the  above  method  takes  advantage  of  this  resistance. 
A  mixture  of  zinc  and  iron  sulphides  can  be  roasted  at  about  600°  C. 
for  as  much  as  two  hours,  causing  but  little  oxidation  of  the  zinc  sul- 


118  FLOTATION 

phide  and  almost  complete  oxidation  of  the  pyrite.  The  ore  does  not 
even  have  to  be  finely  ground  for  this  work  and  can  be  more  easily  pul- 
verized for  notation  after  the  roast  than  before.  I  have  witnessed  a 
separation  of  one  particularly  difficult  ore  containing  marmatite  and 
pyrite.  The  purest  piece  of  marmatite  contained  12%  iron  and  much 
of  it  contained  more.  Of  course,  the  iron  in  the  marmatite  could  not 
be  separated,  but  by  roasting  till  the  iron  from  the  pyrite  was  almost 
completely  converted  into  red  oxide  the  marmatite  could  still  be  floated. 
The  concentrate  assayed  49%  zinc  and  21%  iron,  and  looked  almost 
blood-red.  This  was  made  from  ore  containing  13%  zinc  and  19% 
iron,  which  could  not  be  separated  by  any  other  means,  and  while  the 
flotation  product  was  still  far  too  high  in  iron  to  be  acceptable  at  the 
zinc  smelter,  the  point  to  be  noted  is  the  wonderful  resistance  of  zinc 
sulphide  to  alteration. 

The  question  arises  how  best  to  apply  differential  flotation.  Shall 
a  mixed  flotation  concentrate  of  the  several  sulphides  be  made  first 
and  then  only  this  small  bulk  of  higher-grade  product  be  subjected  to 
differential  flotation  or  would  it  be  better  to  apply  the  differential- 
flotation  methods  to  the  crude  ore? 

It  is  probable  that  a  flow-sheet  in  which  only  a  concentrated  pro- 
duct is  treated  by  the  specialized  methods  described  here  would  allow 
of  more  careful  work,  closer  supervision,  and  the  use  of  more  expensive 
chemicals  than  could  be  applied  to  the  bulk  of  the  crude  ore.  This 
principle  should  apply  to  all  the  methods  in  which  the  previous  con- 
centration by  flotation  dees  not  spoil  the  mineral  particles  for  one  of 
the  differential  schemes.  Such  a  process  as  the  one  in  which  only  a 
minute  amount  of  oil  is  added  to  float  the  galena  of  the  ore,  followed 
by  the  addition  of  more  oil  to  float  the  remaining  sulphides,  would  be 
impossible  if  applied  to  a  mixed  flotation  concentrate  because  this  con- 
centrate already  contains  too  much  oil  for  the  application  of  the  pro- 
cess. It  is  doubtful  if  the  oil  in  a  flotation  concentrate  can  be  removed 
by  any  of  the  proposed  methods  sufficiently  to  warrant  the  applica- 
tion of  this  process.  The  use  of  powdered  carbon  might  be  of  value  in 
this  connection  for  absorbing  some  of  the  excess  oil. 

THE  ELEMENTS  OF  SIMPLICITY  should  be  sought  in  differential  work. 
Any  of  the  methods  of  differential  flotation  that  involve  dewatering 
and  re-pulping  should  be  avoided,  if  possible,  on  account  of  the  space 
and  cost  of  thickeners  and  the  large  amount  of  water  used.  Some 
method  requiring  a  simple  addition  of  oil  or  acid  in  order  to  float  one 
mineral  after  a  first  has  been  floated  will  commend  itself.  Avoid  also 
the  use  of  a  solution  that  can  be  so  changed  by  continual  use  that 


DIFFERENTIAL    FLOTATION  119 

it  sickens  and  has  to  be  discarded.  It  will  be  recalled  that  Owen's  proc- 
ess, using  alkaline  permanganates,  is  one  of  this  type.  A  sodium-sul- 
phide solution  is  likely  to  oxidize  to  thio-sulphates  or  sulphites,  which, 
if  present  in  sufficient  amount,  entirely  inhibit  flotation.  Avoid  the 
use  of  a  solution  of  a  valuable  chemical  that  must  be  washed  out  of 
the  tailing  and  recovered.  The  solution  containing  zinc  chloride  or 
the  one  containing  chromates  is  an  example.  Avoid  the  use  of  addition- 
agents  that,  in  order  to  be  effective,  require  some  length  of  time  in  con- 
tact with  the  ore.  Heating  of  solutions,  unless  by  waste  heat  from  some 
other  operation,  is  also  to  be  avoided.  Finally,  do  not  use  a  method  of 
differential  flotation  that  is  sensitive  and  requires  constant  attention. 

When  differential  flotation  depends  011  the  addition  of  some  chem- 
ical, the  supply  of  that  chemical  and  the  facilities  of  transportation 
to  the  mill  have  to  be  considered.  Sulphuric  acid  is  not  well  adapted  to 
carriage  by  wragon  in  mountainous  districts.  Many  of  the  reagents  are 
expensive  when  bought  on  the  market  but  they  can  be  cheaply  made 
at  the  mine.  For  example,  I  have  heard  Owen's  alkaline  permanganate 
solution  decried  on  the  ground  that  "potassium  permangajite  is 
entirely  too  expensive  a  chemical  for  commercial  work. ' '  No  one  said 
that  the  potassium  salt  had  to  be  used  and  Owen's  claim  was  that  most 
manganese  compounds  were  suitable.  Manganese  ores  are  often  avail- 
able locally  and  the  fusion  of  some  of  this  ore  with  crude  soda  will  give 
an  inexpensive  sodium  manganate.  Lime  is  a  cheap  chemical,  easily 
available  in  most  mining  districts,  and  hydrogen  sulphide  can  be  made 
from  pyrite,  other  sulphides,  or  even  elemental  sulphur.  Likewise, 
sodium  chloride,  common  salt,  is  well  distributed  over  the  face  of  the 
earth  and  is  not  far  distant  from  most  mines.  The  chromates  are  the 
only  reagents  recommended  that  might  be  difficult  to  obtain. 

There  is  only  one  case  where  a  substitute  for  differential  flotation 
seems  to  be  having  any  success,  namely,  in  the  separation  of  the  zinc 
and  lead  sulphides.  A  pulp  that  will  not  separate  well  by  ordinary 
tabling  methods  may  yield  to  a  method  wherein  the  mixed  sulphides  of 
zinc  and  lead  are  floated  together,  the  froth  broken  down,  and  the  pulp 
passed  over  a  Wilfley  or  other  table.  Under  these  conditions  a  streak 
of  lead,  well-defined  and  sharply  differentiated  from  the  zinc,  can  be 
obtained,  whereas  the  gangue-slime  may  prevent  any  gravity-separa- 
tion before  flotation.  Some  people  have  gone  so  far  as  to  believe  that 
the  oiling  of  the  surfaces  of  the  particles  has  improved  the  tabling 
qualities.  It  is  probable  that  the  only  effect  is  the  breaking  up  of  the 
lumps  of  mixed  mineral  during  the  agitation  for  flotation. 

The  most  pressing  problem  in  differential  flotation  is  the  removal  of 


120  FLOTATION 

pyrite  from  a  sphalerite  concentrate  made  by  flotation.  Mixtures  of 
zinc  and  lead  sulphide  are  not  so  hard  to  get  apart.  If  a  previous  frac- 
tional roast  is  given  before  milling  there  is  usually  no  difficulty  from 
the  flotation  of  iron,  and  the  zinc  will  still  float ;  but  if  flotation  is  used 
in  a  wet  mill  to  treat  only  the  slime,  and  a  zinc  concentrate  badly  con- 
taminated with  iron  is  formed,  the  separation  of  the  iron  will  be  diffi- 
cult indeed.  The  most  successful  addition-agents  for  dropping  the  iron 
during  flotation  seem  to  be  oxidizers  like  the  chromates  and  chlor- 
ide of  lime.  Chlorine  improves  the  flotation  of  sphalerite  and  lime 
tends  to  drop  iron.  Copper  sulphate  likewise  seems  to  improve  the 
flotation  of  sphalerite  but  at  the  same  time  tends  to  improve  that  of 
pyrite.  Fortunate  is  he  who  has  the  ore  in  which  the  pyrite  does  not 
tend  to  slime  to  the  same  extent  as  does  the  sphalerite,  or  where  the 
pyrite  is  already  weathered  to  a  condition  in  which  it  is  difficult  to 
float.  At  Crown  King,  Arizona,  a  mixed  flotation  concentrate  of 
zinc  and  iron  sulphides  is  passed  over  a  Wilfley  table  with  the 
result  that  the  oil  is  washed  off  of  the  pieces  of  pyrite.  On  subject- 
ing this  pulp  to  a  second  treatment  only  the  sphalerite  is  floated. 

SUMMARY.  The  factors  used  in  differential  flotation  either  to  as- 
sist the  flotation  of  one  particular  mineral  or  to  retard  its  flotation  are 
tabulated  for  four  of  the  principal  sulphide  minerals.  These  are 
the  factors  on  which  the  various  processes  are  based.  The  abbre- 
viations 'As'  and  'Ret'  mean  'assisted'  and  'retarded'  respectively. 

Sphalerite         Galena  Pyrite       Chalcopyrite 

Factor  As.      Ret.       As.      Ret.      As.      Ret.       As.     Ret. 

Acids *  *  * 

Weakly  alkaline  solutions. . . 

Lime  

Sodium  sulphide  

Chloride  of  lime * 

Chlorine   * 

Limitation  of  oil 

Chromates 

Permanganates,  etc 

Neut.  or  alk.  chlorides 

Weakly  acid  chlorides 

Sulphur  di-oxide,  etc 

Roasting  or  weathering 

Dry  grinding  

Heated  solutions * 

Fine  grinding    

Zinc  chloride  and  HC1 * 

Metallic  Cu  and  Hg. * 

Copper  sulphate    * 

Reducing  solutions    

Oxidizing  solutions    * 

Aeration    

Washing  in  fresh  water 


FLOTATION    OILS  121 

FLOTATION-OILS 

By  0.  C.  RALSTON 
(Written  especially  for  this  volume) 

INTRODUCTION.  Recently  there  have  been  developed  methods  of 
flotation  by  gas-bubbles,  without  a  frothing-agent ;  however,  most  of 
the  successful  frothing  methods  depend  more  directly  on  the  oil  than 
on  any  other  factor.  The  term  'oil'  is  retained  because  most  of  the 
substances  now  in  use  are  of  oily  consistence  even  though  they  may 
not  be  true  oils.  For  example,  carbolic  acid,  which  is  soluble  in  water, 
is  rarely  called  an  'oil'  but  in  flotation  it  functions  as  one. 

Perhaps  the  deepest  mystery  in  flotation  is  the  real  function  of  the 
oil.  While  we  have  theorized  successfully  in  many  directions  we  .are 
still  much  in  the  dark  as  to  just  what  it  does.  We  know  that  if  a 
certain  oil  is  added  in  small  amount  to  an  ore-pulp  the  valuable  min- 
erals are  caught  by  air-bubbles  introduced  into  the  pulp,  and  carried 
by  them  to  the  surface  in  the  form  of  a  froth.  It  has  also  been 
noticed  that  sundry  'oils'  cause  a  great  deal  of  foaming  but  they 
seem  to  carry  very  little  mineral  with  them  to  the  surface.  Moreover, 
it  has  been  found  that  there  are  oils  which  cause  very  little  froth  but 
the  froth  formed  is  heavily  laden  with  mineral.  Therefore,  frothing- 
agents  have  come  to  be  placed  in  two  general  classes,  'frothers'  and 
'collectors.' 

(1)  Frothers.  These  oils  (and  other  agents)  seem  to  be  necessary 
in  order  to  give  some  oils  a  frothing  quality.  It  is  believed  that 'their 
principal  function  is  to  form  froth  of  a  more  or  less  persistent  nature 
by  giving  the  water  in  the  pulp  a  variable  surface-tension.  Literature 
on  the  physics  of  foaming  solutions  informs  us  that  a  pure  liquid  will 
not  froth  or  foam.  The  addition  of  the  proper  contaminant  will 
modify  it  so  that  it  can  form  a  foam.  Such  a  contaminant  must  not 
only  alter  the  surface-tension  of  the  liquid  but  must  be  capable  of  ad- 
justing itself  in  concentrations  so  that  the  surface-tension  developed 
at  any  particular  portion  of  a  bubble  will  be  just  sufficient  to  balance 
the  strain  put  on  the  bubble.  To  illustrate,  let  us  assume  a  soap- 
bubble  hanging  from  the  pipe  on  which  it  was  blown.  It  is  evident 
that  the  portion  of  the  bubble  near  this  point  of  support  must  carry 
the  weight  of  the  bubble  below  and  that  it  is  under  a  greater  strain 
than  the  portions  of  the  film  at  the  bottom  of  the  bubble.  If  the  soap 
adjusts  itself  into  the  different  parts  of  the  bubble  in  the  right  amount 


122  FLOTATION 

to  cause  the  surface-tension  of  the  water  to  change  enough  to  balance 
the  strain  put  on  the  film  at  each  point,  we  have  the  conditions  for 
persistence  of  froth.  In  the  case  considered,  since  soap  reduces  the 
surface-tension  of  the  water,  the  greatest  concentrations  of  soap  will 
be  found  in  the  lowest  portions  of  the  bubble  where  the  strain  is  least 
and  consequently  it  is  there  that  the  surface-tension  is  lowered  the 
most.  The  common  f rothers  now  used  are  the  products  of  the  distilla- 
tion of  wood,  such  as  pine-oil,  pine-creosote,  hardwood-creosote,  turp- 
entine, and  resin-oil,  as  well  as  certain  coal-tar  fractions  like  phenol, 
cresol,  and  the  tar-acids. 

(2)  Collectors.  As  mentioned  above,  some  oils  seem  to  be  adapted 
to  making  froth  yet  do  not  collect  much  mineral  into  the  froth.  Other 
oils  seem  to  be  specially  adapted  to  collecting  the  mineral  but  little 
adapted  to  frothing.  The  addition  of  a  collecting-oil  to  a  frother 
usually  results  in  a  froth  more  heavily  burdened  with  mineral.  As  a 
rule,  the  frothers  are  either  soluble  in  the  water  or  form  colloidal 
emulsions,  which  also  alter  the  surface-tension  of  water.  The  col- 
lectors are  usually  much  less  soluble  in  water  and  seem  to  concentrate 
on  the  surfaces  of  mineral  particles  so  as  to  'oil'  them.  The  common 
collectors  are  coal-tar,  coal-creosote,  pine-tar,  hardwood-tar,  crude 
petroleum  and  many  of  its  fractions. 

All  oils  possess  both  some  frothing  and  some  collecting  ability  and 
many  of  them  are  acceptable  for  performing  both  functions.  Eucalyp- 
tus-oil and  pine-oil  are  examples  of  this  latter  type. 

CONDITION  OF  THE  OIL.  It  seems  necessary  to  distribute  the  oil 
intimately  through  the  pulp  before  successful  flotation  takes  place. 
In  doing  this  the  oil  almost  entirely  disappears  for  the  reason  that  it 
is  rarely  used  in  amounts  of  over  four  pounds  per  ton  of  ore  and  often 
less  than  a  pound  of  oil  per  ton  of  ore  is  used.  Flotation-men  call  this 
distribution  of  the  oil  through  the  pulp  'emulsification,'  but  a  ques- 
tion has  been  raised  as  to  the  correctness  of  this  terminology.  Un- 
doubtedly the  oil  is  very  finely  divided  but  whether  '  emulsified, '  as  the 
chemist  would  see  it,  is  doubtful.  In  fact,  G.  D.  Van  Arsdale  shows1 
that  there  are  generally  present  in  a  flotation-pulp  enough  dissolved 
electrolytes  or  other  agents  to  prevent  emulsification.  The  flocculation 
of  suspensions  and  the  coagulation  of  emulsions  by  certain  electro- 
lytes are  well  known  in  colloid  chemistry.  Materials,  such  as  tanninc, 
which  promote  emulsification,  seem  to  prevent  flotation.  Van  Arsdale 
has  also  made  an  interesting  observation  on  mixing  a  collecting  and 
frothing  oil.  If  a  film  of  collecting-oil  is  formed  by  placing  a  drop  of 


.  iO  Min.  Jour.,  May  13,  1916. 


FLOTATION    OILS  123 

it  on  the  surface  of  water,  it  spreads  over  a  large  area.  By  dropping 
in  a  small  amount  of  a  frothing-oil  the  immediate  retraction  of  this 
film  is  claimed  and  the  collecting-oil ' '  takes  on  a  circular  globular  form 
with  a  definite  positive  contact-angle."  This  leads  Van  Arsdale  to 
believe  that  if  a  collecting-oil  has  adhered  to  a  particle  of  mineral  arid 
a  frothing-oil  is  later  added,  flotation  should  be  immediately  improved. 

Wilder  D.  Bancroft,  with  his  usual  lucidity,  seizes  on  what  Van 
Arsdale  says  and  recognizes  in  it  the  condition  for  the  formation  of 
emulsions  of  water  in  oil  instead  of  oil  in  water.  He  deduces  that  any 
addition  agent  which  tends  to  increase  dispersion  in  the  oil  phase  and 
to  decrease  it  in  the  water  phase,  will  assist  flotation.  Hence  we  can 
understand  why  Bancroft  believed  that  flotation  was  "nothing  but  a 
special  case  in  emulsions."2 

It  is  highly  probable  that  some  of  the  frothing-oil  is  dissolved  in 
the  water.  Where  mills  dewater  the  tailing  and  return  the  water  to  the 
mill,  often  this  water  needs  no  addition  of  a  frothing-agent.  However, 
a  collector  must  be  added  because  flotation  in  this  water  brings  up 
very  little  mineral.  Hence,  the  supposition  that  the  collecting-oil  is  in- 
soluble and  that  it  has  adhered  to  the  sulphide  and  thereby  left  the 
frothing-agent  in  the  solution.  A  striking  confirmation  of  this  is 
found  in  a  couple  of  experiments  performed  in  court  in  the  Miami 
case  by  Dr.  Liebmann,  witness  for  Minerals  Separation.  He  concen- 
trated Broken  Hill  tailing  with  oleic  acid  (insoluble)  as  a  flotation- 
agent  and  then  repeatedly  washed  the  concentrate  with  hot  water. 
On  submitting  this  concentrate  to  flotation  in  fresh  water  and  without 
the  addition  of  any  more  flotation-agent  the  mineral  was  re-floated, 
showing  that  the  oleic  acid  had  stuck  to  it.  When  phenol  was  used  in 
a  similar  experiment  only  20%  of  the  concentrate  could  be  re-floated, 
showing  that  the  soluble  phenol  had  been  washed  away  from  the  con- 
centrate. 

PERSISTENCE  OF  FROTH.  The  prime  requisite  for  a  persistent  froth 
is  a  variable  surface-tension  of  the  water.  Some  practical  observa- 
tions on  the  conditions  favorable  to  either  brittle  or  persistent  froth 
are  next  in  order.  Pine-oil  and  many  other  single  oils  tend  to  give  a 
fairly  brittle  froth.  Oils  that  contain  a  great  many  different  sub- 
stances and  mixtures  of  oil  yield  a  more  persistent  froth.  The  wood- 
creosotes  usually  give  a  more  lasting  froth  in  which  the  bubbles  obtain 
a  larger  size  than  is  the  case  with  pine-oil.  As  a  rule,  the  better  the 
oil  is  distributed  through  the  pulp  the  more  stable  is  the  froth. 

The  persistence  of  the  froth  in  a  'mechanical'  machine,  as  corn- 


*Met.  &  Chem.  Eng.,  June  1,  1916. 


124  FLOTATION 

pared  with  the  evanescent  froth  produced  in  the  'pneumatic'  machine, 
has  led  to  much  conjecture  concerning  the  cause  of  the  difference. 
The  following  proposed  explanation  is  rather  simple.  In  the  pneu- 
matic machine  so  much  air  is  introduced  that  only  a  few  mineral  par- 
ticles are  found  clinging  to  each  bubble.  At  the  surface  of  the  froth 
these  numerous  bubbles,  in  bursting,  drop  their  burdens  on  the  bub- 
bles below  them  and  if  the  froth  is  allowed  thus  to  collect  mineral 
without  overflowing  it  usually  assumes  the  condition  of  the  more 
persistent  froth  in  a  mechanical  agitator ;  in  other  words,  a  pneumatic 
froth  carries  less  mineral  but  contains  more  water  and  air.  In  the 
mechanical  agitator  each  bubble  of  air  is  usually  well  loaded  because 
there  are  fewer  of  them  and  the  mineral  particles  come  so  close  to 
each  other  that  they  mat  together  and  tend  to  support  the  arch  of  the 
bubble.  If  allowed  to  dry  without  disturbance  they  will  dry  into  mud 
of  the  same  shape  as  the  original  bubbles  of  froth.  In  fact,  many  per- 
sistent froths  could  almost  be  called  mud-froths.  Of  course,  the  proper 
frothing-agent  will  give  the  desired  variability  of  surface-tension  to 
the  water,  irrespective  of  the  mineral  burden.  Instances  are  known 
of  the  proper  oil-mixtures  being  obtained  to  give  such  a  tough  froth 
that  the  mill-floor  would  be  flooded  many  feet  deep  with  it  before  the 
trouble  could  be  righted  by  cutting  down  the  oil-feed  or  changing  its 
composition. 

OVER-OILING.  In  any  mill  that  has  been  brought  to  a  high  state 
of  efficiency  by  use  of  a  definite  proportion  of  an  oil  mixture  and  under 
given  conditions  of  agitation,  an  excess  of  oil  causes  a  bad  effect.  This 
effect  is  much  less  pronounced  with  collecting-oils  than  with  frothing- 
oils.  When  the  over-oil  effect  is  noticed  the  froth  is  usually  'dirty;' 
it  contains  too  much  gangue.  The  remedy  is  more  agitation  (at  least 
a  change  in  agitation)  in  order  properly  to  distribute  the  excess  of 
oil.  The  basic  patent  of  Minerals  Separation  was  recently  hel$  valid 
in  the  Supreme  Court  on  the  ground  that  they  had  shown  a  new  effect 
when  less  than  1%  of  oil  was  used,Aand  hence  they  were  entitled  to 
patent-rights.  Many  people  have  held  the  opinion  that  the  over-oil 
effect  plainly  showed  that  more  than  1%  would  give  a  poor  metal- 
lurgical result  and  a  different  kind  of  froth.  As  a  matter  of  fact,  the 
over-oil  effect  appears  only  when  changing  the  amount  of  oil  used  and 
not  the  other  conditions  of  flotation.  Just  as  it  usually  takes  consider- 
able adjustment  of  plant  to  get  good  results  when  using  one  pound 
of  oil  per  ton,  a  similar  adjustment  of  conditions  is  necessary  before 
25  or  50  pounds  of  oil  per  ton  of  ore  can  be  used  with  success.  Since 
the  decision  of  the  Supreme  Court  was  published  several  companies 


FLOTATION    OILS  125 

have  been  using  more  than  1%  of  oil  without  making  any  apparent 
difference  in  the  froth  produced.  In  fact,  the  data  given  out  on  the 
operations  of  the  slime-plant  at  the  Arthur  mill  of  the  Utah  Copper 
Company  show  that  a  somewhat  higher  extraction  and  a  higher  grade 
of  concentrate  is  now  being  produced  with  32  Ib.  of  oil  as  compared 
with  the  former  2  to  4  Ib.  per  ton  of  ore.  Moreover,  the  machines  are 
not  as  sensitive  to  changes  in  the  feed.  The  metallurgical  result  is  the 
same  or  better ;  the  physical  appearance  of  the  froth  is  the  same,  and 
only  the  increased  odor  of  oil  in  the  mill  would  indicate  the  use  of  any 
more  than  the  usual  proportion  of  oil.  Of  course,  the  *  emulsification ' 
had  to  be  taken  into  account  when  the  amount  of  oil  was  increased. 
The  oil  used  is  a  crude-topped  petroleum  with  a  small  amount  of  coal- 
tar  and  of  pine-oil.  This  is  a  large-scale  verification  of  the  claim  made 
by  the  defendants  in  the  Hyde  case  that  the  use  of  less  than  1%  of  oil 
was  merely  for  economy  and  hence  not  a  patentable  process.  The 
defendants  produced  the  regular  froth  in  an  experimental  machine  be- 
fore the  court,  when  using  successive  increases  up  to  25%  of  oil  on  the 
weight  of  the  ore.  However,  the  plaintiffs  succeeded  in  convincing  the 
judges  that  this  was  merely  a  laboratory  trick  and  that  there  was  a 
new  effect  produced  by  the  use  of  less  than  1%  of  oil.  Minerals 
Separation  claimed  to  have  made  75-ton  tests  on  the  use  of  more  than 
1%.  of  oil  and  that  the  results  showed  a  low  extraction  and  a  poor 
grade  of  froth.  It  is  probable  that  they  operated  the  large  plant  long 
enough  to  produce  only  the  'over-oil'  effect  and  that  they  did  not  ad- 
just the  operation  of  the  plant  to  the  increased  amount  of  oil.  This 
was  merely  negative  evidence. 

RAW  OIL  EFFECT  is  a  striking  phenomenon,  which  was  first  men- 
tioned by  W.  A.  Mueller.3  A  good  froth  can  be  killed  instantly  by 
pouring  on  it  a  small  amount  of  the  same  oil  that  was  used  in  making 
the  froth.  It  not  only  makes  a  hole  through  the  froth  in  the  immediate 
neighborhood  of  the  raw  oil  but  the  oil  may  even  spread  over  the  whole 
surface  of  the  cell.  Not  until  this  raw  oil  has  been  well  stirred  into  the 
pulp  can  a  good  froth  be  formed  again. 

CHOICE  OF  OIL.  The  maximum  economic  effect  requires  that  the  oil 
or  mixtures  of  oil  chosen  must  produce  the  highest  grade  of  concentrate 
with  the  highest  possible  recovery  for  the  minimum  cost  and  at  the 
maximum  profit.  In  copper  work  a  low  tailing  is  a  greater  deside- 
ratum than  a  high-grade  concentrate,  while  in  zinc  work  everything 
must  be  done  to  obtain  as  high  a  grade  of  concentrate  as  possible.  In 
any  case,  where  the  concentrate  has  to  be  shipped  a  long  way,  an  oil 


3'Froths  Formed  by  Flotation-Oils,'  Eng.  &  Min.  Jour.,  July  1,  1916. 


126 


FLOTATION 


Pine-creosote. 
Hardwood-oil. 
Hardwood-creosote. 
Hardwood-tar. 


must  be  used  that  will  allow  the  preparation  of  a  clean  concentrate. 
In  order  to  obtain  a  cheap  oil  it  is  now  quite  common  in  most  copper 
work  for  the  mill-men  to  mix  a  high-grade  pine-oil,  or  other  frother, 
with  a  great  excess  of  a  cheap  petroleum  or  a  coal-tar  as  a  collecter. 
The  classes  of  oils  used  are  as  follows : 

PRODUCTS  OF  WOOD  DISTILLATION — 

Pine-oil,  both  steam-distilled  and  destructively  distilled. 

Pine-tar  oil. 

Rosin-oil. 

Pine-tar. 

Turpentine. 

PRODUCTS  OF  DISTILLATION  OF  COAL — 
Coal-creosote. 
Cresol. 
Phenol. 

Coal-tar,  from  gas-works  and  by-product  coke-ovens. 
Water-gas  tar. 

PETROLEUM  PRODUCTS — 

Crude  petroleums  (California,  Texas,  Kansas,  Illinois). 
Distillate,  after  removing  gasoline  and  fuel-oil. 
Fuel-oil,  a  topped  petroleum. 
Kerosene  acid-sludge. 

ANIMAL  OILS  OR  DERIVATIVES — 
Oleic  acid. 

Many  other  oils  have  been  tested  but  they  are  not  in  general  use. 
Among  the  coal-products  the  creosote  and  tar  are  the  only  two  that  are 
important  in  flotation.  Hardwood-creosote  is  the  only  hardwood  frac- 
tion that  is  in  general  use.  Eucalyptus-oil  and  fir-oil  are  used  in 
Australia  and  Canada,  but  hardly  at  all  in  the  United  States. 

CONSUMPTION  OF  OIL.  A  statement  was  issued  by  the  Bureau  of 
Mines  in  May  1916  giving  the  market  conditions  and  the  consumption 
of  flotation-oil  in  the  United  States  at  the  beginning  of  1916  and  the 
estimated  consumption  by  the  beginning  of  1917.  The  following  table 
is  taken  from  that  statement. 


MONTHLY    CONSUMPTION   OF   FLOTATION-OILS    IN   UN/TED   STATES. 

Type 
of 
Ore 

Vonffify  Tonnage.  Ore. 

r~/otation-o//s.     Beginning    of  /9/6.   (In  pounds  per  month.) 

Beginning 
1916 

Beginning 
/9/7 
(estimate) 

Wood   Products 

0/eic 
odd 

Coo/  Products 

Petro/eum 

Pine 
oil 

Pf'ne- 
tor 
o// 

£u- 
co/yp 
fus 

Creosote 

Tur- 
pen- 
tine 

Tar 

Creosote 

Cres- 
o/ 

Crude 

Fractions 

Copper 

(Ton*} 
/,248.OOO 

(Tons) 

/.94Z.OOO 

(fb.) 
S  9.300 

f/6.) 

7SO 

(Jb.) 

(Ib.) 
41  7.OOO 

f/6.) 
/soo 

(/&•) 

(/b.) 

677.000 

f/6-) 
403.000 

C/6  ) 
8.340 

f/6.) 

79  000 

i/6.  ) 
1702.  000 

Zinc  ir 
Complex 

a48.ooo 

350.000 

60,760 

667 

262.600 

3.330 

J830 

/0,670 

46.  SOO 

/57000 

4/.000 

Lead 

//£-,  000 

/36.000 

3.900 

2/6 

/a  /.ooo 

9.SSO 

660 

Go/d  A 
•Silver 

4S.7OO 

/23.000 

9.63O 

75O 

4O,  2SO 

Z7.4SO 

4,920 

7.09O 

6.S-SO 

TOTAL 

/.666.  70  O 

2.  £5/,  OOO 

133.  78O 

^./67 

!L/6 

840.7SO 

4.830 

J.030 

7/S.  /2O 

463.  6  7O 

0.340 

243.  090 

1.  749.  9/O 

FLOTATION    OILS  127 

These  figures  are  the  best  estimates  that  can  be  prepared  to  give  an 
idea  of  the  tonnage  of  ore  now  treated  and  to  indicate  the  new  demand 
on  the  oil-producers.  Three  years  ago  very  few  flotation-mills  were  in 
existence  in  the  United  States.  The  sudden  development  of  the  process 
upset  conditions  in  the  various  oil-markets  so  that  for  a  time  the  pro- 
ducers questioned  their  ability  to  supply  the  demand.  The  beginning 
of  the  War  cut  off  the  supply  of  German-made  coal-creosotes.  Now 
every  company  that  is  producing  any  of  the  best  types  of  oils  is 
figuring  how  to  capture  a  goodly  share  of  the  supply.  Here  is  such  a 
large  outlet  for  some  products  that  an  entirely  new  market  condition 
has  arisen.  Take  the  case  of  pine-oil,  as  an  example.  Before  flotation 
called  for  it,  pine-oil  was  a  drug  on  the  market  and  could  be  bought  at 
reasonable  figures.  The  demand  from  flotation  men  became  too  great 
and  other  oils  had  to  take  its  place.  All  the  available  pine-oil  is  still 
sold  for  prices  rarely  below  50c.  per  gallon.  Many  of  the  oils  now 
called  'pine-oils'  are  not  the  pine-oil  of  the  U.  S.  Navy  specifications, 
but  simply  oils  prepared  by  distilling  pine-wood. 

DISTILLATION  OF  PINE- WOOD.  Undoubtedly  some  of  the  most  valu- 
able oils  for  flotation  today  are  the  various  oils  that  come  from  the 
distillation  of  pine-wood.  The  wood-distillation  industry  in  the  east- 
ern South  is  taking  for  a  crude  material  what  is  known  as  the  fat 
lightwood — the  dead  timber  and  the  stumps  from  former  logging 
operations.  Only  the  dead  wood  contains  much  pine-oil,  as  a  result  of 
the  oxidation  and  other  changes  that  take  place  in  the  sap. 

Two  main  methods  of  distillation  are  recognized,  steam  distillation 
and  destructive  distillation.  In  the  steam-distillation  of  pine-wood,  the 
wood  is  'hogged'  into  chips  and  live  steam  is  passed  through  the  wood 
in  a  retort.  A  crude  turpentine  is  distilled  and  the  chips  are  then 
ready  for  the  extraction  of  the  resin  by  means  of  a  solvent  like  gaso- 
line, after  which  they  are  made  into  paper,  thrown  away,  or  .burned. 
The  crude  turpentine  is  the  only  distillate  produced  in  this  case  and 
is  condensed  with  the  steam  issuing  from  the  retorts.  This  crude  tur- 
pentine is  then  separated  into  pure  wood-turpentine  and  pine-oil. 
The  latter  is  the  'steam-distilled'  pine-oil  of  commerce.  It  has  a 
higher  boiling-point  than  the  turpentine  and  is  easily  separated  from 
it.  This  steam-distilled  pine-oil  is  one  of  the  best  flotation-oils  made 
in  the  United  States  and  only  about  175,000  Ib.  of  it  is  produced  per 
month.  Of  this  three-fourths  goes  into  the  chemical  trades  and  the 
remainder  into  flotation. 

In  the  destructive  distillation  of  pine-wood  it  is  placed  in  closed 
retorts  and  heated  with  a  fire.  The  wood  is  reduced  to  charcoal  and 


128  FLOTATION 

the  crude  distillate  is  composed  of  four  things:  gas  which  escapes, 
crude  pyroligneous  acid,  crude  turpentine,  and  crude  tar.  The  tur- 
pentine is  in  the  first  fraction  distilled;  the  tar  settles  out  of  the 
pyroligneous  acid,  which  consists  mostly  of  water  but  contains  acetic 
acid  and  wood-alcohol  as  the  principal  dissolved  constituents.  The 
crude  turpentine,  which  is  all  distilled  by  the  time  the  retort  reaches 
275°  C.,  is  separated  by  distillation  into  what  is  known  as  destruc- 
tively distilled  turpentine  and  destructively  distilled  pine-oil.  Much 
more  of  this  kind  of  pine-oil  is  available  than  there  is  of  steam-dis- 
tilled pine-oil  and  it  can  be  purchased  for  a  lower  price.  Being  a 
destructively  distilled  product  it  naturally  contains  some  of  the  other 
products  of  destruction  of  the  wood,  such  as  pine-tar  oil  and  resin-oil. 
The  crude  tar — distilled  from  the  wood — is  re-distilled  to  give  some  of 
the  crude  turpentine  that  was  caught  with  it  some  more  crude  pine- 
oil,  a  great  amount  of  pine-tar  oil,  and  finally  pine-pitch.  Much  of  the 
pine-tar  oil  is  used  by  the  flotation  trade  under  the  impression  that 
it  is  pine-oil.  From  one  cord  of  4000  Ib.  of  pine-wood  there  is  usu- 
ally obtained  about  10  gallons  of  'd.d.  turp.,'  3  gal.  pine-oil,  40-50 
gal.  pine-tar  oil,  and  20-25  gal.  pitch.  The  pyroligneous  acid  amounts 
to  125-150  gal.  and  the  charcoal  weighs  800  Ib.  It  can  thus  be  seen 
that  the  principal  oil-product  produced  by  the  resinous-wood  distiller 
is  pine-tar  oil.  Pine-tar  oil  is  not  pine-tar.  It  is  an  oil  obtained  by 
distilling  pine-tar.  Likewise,  resin-oil  is  an  oil  obtained  by  distilling 
resin  destructively  and  is  usually  contained  in  pine-tar  oil.  True 
pine-oil  and  turpentine  existed  as  such  in  the  wood  before  it  was  dis- 
tilled. The  other  products  result  by  the  breaking  up  of  the  wood. 

In  the  distillation  of  hard  wood  much  the  same  thing  happens  as 
in  the  destructive  distillation  of  resinous  wood.  A  charcoal,  a  tar,  and 
a  gas  product  are  obtained  together  with  the  pyroligneous  acid.  The 
pyroligneous  acid  is  worked-up  into  acetic  acid  and  wood-alcohol.  The 
tar  settles  out  of  the  pyroligneous  acid  and  is  called  the  'settled  tar.' 
There  is  also  a  portion  of  the  tar  dissolved  in  the  pyroligneous  acid 
and  called  dissolved  tar,  which  is  recovered  by  boiling  away  the 
alcohol,  water,  etc.  This  dissolved  tar  is  different  from  the  settled 
tar.  The  settled  tar  is  distilled  by  use  of  steam-heat  and  a  light 
'wood-oil'  separates  from  the  rest  of  the  tar.  The  remainder  is  dis- 
tilled over  a  direct  fire,  giving  a  'light'  oil,  a  'heavy'  oil,  and  pitch. 
The  heavy  oil  is  emulsified  in  water  with  sodium  hydrate,  the  in- 
soluble portion  withdrawn,  and  the  solution  then  mixed  with  sulphuric 
acid,  which  throws  out  'creosote'  and  leaves  a  solution  of  sodium 
sulphate. 


FLOTATION    OILS 


129 


Nearly  all  of  the  above-mentioned  fractions  from  wood-distillation 
are  sold  on  the  market  for  flotation  work  and  in  many  cases  the  crude 
intermediate  products  are  acceptable  without  further  refining.  The 
hardwood-creosotes  and  tars  can  be  obtained  cheaply  as  several  million 
gallons  of  each  are  annually  used  merely  as  fuel. 

PHYSICAL  AND  CHEMICAL  PROPERTIES  of  some  of  these  oils  have 
been  given  in  the  trade-circulars  of  a  number  of  dealers.  These  have 
been  prepared  in  an  honest  attempt  to  standardize  the  oils  sold  and 
prevent  the  difficulties  met  in  the  flotation-mills  when  oil  shipments 
cannot  be  duplicated. 

The  Pensacola  Tar  &  Turpentine  Co.  is  a  distiller  of  soft  wood, 
using  destructive  distillation.  I  quote  the  table  of  physical  constants 
of  their  flotation-oils.  These  constants  represent  the  properties  of 
similar  wood-oils  sold  by  other  dealers. 

Specific 
No.  Name  gravity 

75  Crude  wood-turpentine.  .0.887 

80  Crude  pine-oil    0.911 

90  Pine-tar  oil,   re-distilled. 0.982 

200  Refined  wood-creosote. .  .0.965 

400  Crude    wood-creosote. . .  .1.025 

15  Thin  resin-oil   1.017 

350  Crude   pine-wood   oil 1.019 

1580  Combination  pine-oil 0.980 

The  non-polymerizable  matter  is  that  which  will  not  be  dissolved 
in  concentrated  sulphuric  acid.  The  test  mentioned  in  the  last  column 
is  the  one  used  by  organic  chemists  in  order  to  give  an  idea  of  the 
amount  of  mineral-oil  that  may  have  been  added  as  an  adulterant. 
The  greater  the  non-polymerizable  residue,  the  more  mineral-oil  prob- 
ably present.  The  test  is  particularly  adapted  to  testing  turpentine 
and  light  oils,  and  is  conducted  as  follows : 

"  Place  20  c.c.  of  concentrated  sulphuric  acid  in  a  graduated 
narrow-neck  Babcock  flask,  and  place  in  ice-water  or  other  cold  water 
to  cool.  Add  slowly  about  5  c.c.  of  the  oil  to  be  tested.  Gradually 
mix  the  contents,  cooling  from  time  to  time,  not  allowing  the  tem- 
perature to  rise  above  60 °C.  When  it  no  longer  warms  on  shaking, 
agitate  thoroughly.  Place  in  water-bath  and  heat  to  60°  or  65°  for 
about  ten  minutes.  Keep  agitating  four  or  five  times  during  the  heat- 
ing. Cool  to  room  temperature  and  fill  the  flask  with  concentrated 
sulphuric  acid  until  the  unpolymerizable  matter  rises  in  the  neck. 
Allow  to  stand  12  hours  or  more  for  light  oils  and  48  for  heavier  ones, 
and  read  unpolymerizable  matter  in  graduated  neck  for  percentage. 
Note :  The  longer  period  is  to  be  preferred,  as  it  often  takes  time  to 


Non-poly- 

Distilling  Refractive  Vis- 

meriz- 

points          index      cosity 

able 

65-217°C.     1.456           0.9 

10-12% 

70-232          1.4894         1.1 

8 

160-368          1.5636         5.8 

Note 

105-275          1.5096         1.7 

7-8 

190-360          1.4977         2.9 

Note 

170-368          1.5631         6.1 

Note 

70-345          1.525           2.9 

4 

85-352           1.5361         2.3 

Note 

130  FLOTATION 

make  the  separation.  All  the  organic  oils  contain  some  unpolymeriz- 
able  oil,  which  should  be  deducted. ' ' 

A  second  test  is  for  heavier  oils,  such  as  tar-oils  and  resin-oils.  It 
is  known  as  the  acetic  acid  test  and  is  conducted  as  follows :  * '  Weigh 
about  40  grammes  of  the  oil  into  an  evaporating-dish,  then  add  100 
c.c.  of  10%  alcoholic  potash  solution  and  heat  on  a  water-bath  for  15 
minutes,  stirring  well.  This  mass  is  then  poured  into  a  separating- 
funnel  and  the  soap  washed  out  with  water.  The  unsaponifiable  mat- 
ter is  then  run  into  a  flask  with  100  c.c.  of  glacial  acetic  acid  and 
heated  to  52  °C.,  shaking  the  flask  to  dissolve  the  soluble  matter.  This 
mixture  is  then  run  into  a  separating-funnel,  using  a  little  acetic  acid 
to  wash  out  the  flask,  and  allowed  to  stand  about  30  minutes,  when 
most  of  the  mineral-oil  will  be  separated  on  top.  After  separating, 
the  solution  should  be  put  back  into  the  funnel,  as  there  may  be  more 
separation,  in  which  case  it  is  separated  and  added  to  the  rest  of  the 
mineral-oil,  which  has  been  run  into  a  weighed  beaker  and  placed 
on  the  water-bath  to  evaporate  the  acetic  acid.  The  beaker  containing 
the  separated  oil  is  weighed  and  is  considered  mineral-oil;  this  can 
be  ascertained  by  the  odor  and  by  treating  with  concentrated  sul- 
phuric acid." 

Both  of  the  above  tests  are  now  commonly  used  in  the  labora- 
tories of  the  larger  companies  using  flotation.  Their  utility  has  been 
great  and  has  enabled  these  companies  to  refuse  shipments  of  adulter- 
ated oil,  the  adulterants  commonly  being  non-polymerizable  mineral- 
oils. 

The  General  Naval  Stores  Co.  has  likewise  compiled  some  useful 
data  about  oils  from  which  the  following  is  abstracted.  It  gives  an 
excellent  idea  of  the  particular  field  in  which  each  oil  has  proved  of 
practical  utility.  (See  next  page.) 

The  sludge-acids  from  refineries  treating  petroleum,  coal-tar,  and 
other  oily  products  constitute  another  series  of  products  that  have 
been  misunderstood  by  mill-men.  They  are  mixtures  of  concentrated 
sulphuric  acid  with  portions  of  the  oils  that  have  been  refined.  For 
instance,  in  the  refining  of  kerosene  the  treatment  with  strong  sul- 
phuric acid  will  dissolve  certain  tarry  or  asphaltic  constituents,  leav- 
ing it  water-white.  These  sulphonated  oil  compounds  are  commonly 
wasted  by  the  refineries.  The  material  can  be  bought  cheaply  as  a 
thick  black  liquor,  often  containing  the  equivalent  of  50%  sulphuric 
acid  by  weight.  Of  course,  other  oils  than  kerosene  are  treated  by 
this  method  during  refining,  but  it  so  happens  that  the  kerosene-acid 
sludge  has  proved  of  greater  value  than  the  others.  Kerosene  sludges 


FLOTATION    OILS 


131 


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132  FLOTATION 

t 

produced  by  different  refineries  differ  in  their  flotation  value,  and 
the  Californian  oil-sludges  are  the  only  ones  that  seem  to  have  given 
satisfaction  in  flotation  plants. 

It  is  probable  that  credit  for  the  discovery  of  the  flotative  value 
of  these  sludges  belongs  to  Minerals  Separation.  At  least  this  com- 
pany owns  the  patents  covering  its  use  (U.  S.  1,170,637,  granted  to 
A.  H.  Higgins).  The  patent  specification  claims  the  sulphuric  acid 
derivatives  of  fats,  oils,  alcohols,  phenols,  and  their  homologues. 
Flotation  in  the  slightly  acid  pulp  with  the  above  compounds  as 
frothing  agents  gives  different  results  from  the  use  of  these  oils  after 
sulphonating  with  strong  acid.  A  second  patent,  covering  the  use  of 
sludges  obtained  from  petroleums,  kerosene,  gas-tar,  etc.,  was  granted 
to  E.  H.  Nutter  (U.  S.  1,170,665).  This  patent  cites  the  use  of 
kerosene-acid  sludge  at  Anaconda,  which  is  the  greatest  user  of  the 
product.  Not  over  a  half-dozen  other  companies  are  using  it.  In 
every  case  a  pyritiferous  mineral  is  being  floated.  These  sludges  are 
said  to  do  good  work  in  sub-aeration  machines.  Sometimes  they  work 
better  if  they  have  been  standing  awhile,  or  after  they  have  been  mixed 
with  water. 

In  case  sulphuric  acid  will  not  dissolve  an  oil,  it  is  sometimes  pos- 
sible to  dissolve  it  in  strong  acetic  acid  and  then  add  the  sulphuric 
acid.  Most  significant  is  the  fact  that  most  of  the  good  frothing-oils 
are  almost  completely  polymerizable  by  this  method.  This  indicates 
that  the  sludge-acid  is  nothing  but  a  concentrated  form  of  the  poly- 
merizable material  present  in  small  amounts  in  crude  petroleum  and 
other  oils.  A  further  conclusion  is  that  the  presence  of  'double  bonds' 
in  the  molecules  of  the  oils  used  is  essential  to  their  becoming  good 
frothers.  The  fact  that  carbolic  acid  is  a  better  flotation-oil  than 
oleic  acid  should  be  interesting  to  organic  and  physical  chemists. 

Another  bit  of  theory  in  connection  with  the  acid-sludges  and  the 
sulphonated  oils  has  to  do  with  the  idea  that  acid  is  necessary  to  clean 
the  surfaces  of  sulphides  that  have  commenced  to  oxidize.  By  using 
a  sulphonated  oil  the  acid  cleans  the  surface  of  a  sulphide  particle  and 
the  oil  is  present  in  the  most  advantageous  position  to  'oil'  the  cleaned 
surface. 

The  search  for  new  flotation-oils  is  still  keen.  Because  we  do  not 
yet  know  what  differences  in  oils  makes  one  good  and  the  other  bad, 
the  only  method  available  for  carrying  on  this  work  is  to  obtain 
samples  of  the  thousands  of  products  and  mixtures  that  are  on  the 
market  and  test  them  on  a  given  ore  in  comparison  with  oils  of  known 
value  for  flotation.  In  Australia  it  was  found  that  many  of  the 


FLOTATION    OILS  133 

eucalyptus-oils  high  in  phlanderene  were  best,  especially  for  differ- 
ential flotation,  but  phlanderene  cannot  be  found  in  many  of  the 
American  pine-oils  that  are  standard. 

Sage-brush  oil  was  discovered  to  be  an  excellent  flotation-oil 
through  some  co-operative  work  between  Maxwell  Adams,  of  the 
University  of  Nevada,  and  the  Salt  Lake  City  station  of  the  Bureau 
of  Mines.  G.  H.  Clevenger  also  took  up  the  distillation  of  sage-brush 
and  tested  the  oil  resulting  therefrom.  Papers  by  both  Adams  and 
Clevenger  were  read  at  the  Globe  meeting  of  the  American  Institute 
of  Mining  Engineers  and  published  in  Bulletin  117  of  the  Institute. 
My  own  discussion  of  the  probable  cost  of  production  of  sage-tar  ap- 
peared in  Bulletin  119.  It  is  there  shown  that  it  can  probably  be 
produced  for  from  30  to  50  cents  per  gallon,  and  since  it  is  the  full 
equivalent,  if  not  the  superior,  of  steam-distilled  pine-oil,  its  future 
production  in  the  semi-arid  regions  where  sage-brush  is  abundant 
would  seem  justified.  It  is  particularly  valuable  for  the  flotation  of 
sulphidized  'carbonate'  ores. 


IT  is  DIFFICULT  to  utilize  coal-tar  in  plants  using  flotation  supple- 
mentary to  gravity  concentration,  on  account  of  the  fact  that  it  is  not 
easy  to  effect  a  good  amalgamation  of  tar  with  the  pulp  in  agitating- 
tanks,  and  even  in  mechanical  flotation-machines.  The  use  of  coal-tar 
lends  itself  very  well  indeed  to  the  system  of  feeding  tar  into  the 
grinding  machines,  a  system  that,  as  mentioned  above,  had  been 
worked  out  in  our  small  test-mill  and  patented  by  G.  A.  Chapman. 

The  company  is  indebted  to  Mr.  J.  M.  Callow  for  proving  the  merits 
of  coal-tar  creosote  as  a  flotation  agent  by  using  it,  in  his  demonstra- 
tion plant  at  Inspiration.  After  we  had  established  the  value  of 
coal-tar  by  laboratory  tests,  and  while  efforts  were  being  made  to 
obtain  it  commercially,  he  applied  creosote  successfully.  We  have 
continued  to  use  it  for  a  long  time,  mostly  in  combination  with  coal- 
tar,  and  have  only  recently  dropped  it,  as  we  find  crude  coal-tar 
cheaper  and  better. — Rudolf  Gahl,  Trans.  A.  I.  M.  E. 


134  FLOTATION 

ORE-FLOTATION 

By  WILDER  D.  BANCROFT 

*When  discussing  the  theory  of  ore-flotation,  people  are  apt  to  lay 
great  stress  upon  surface-tension  in  general  and  upon  contact-angles 
in  particular.  While  this  is  entirely  legitimate,  it  seems  undesirable, 
because  we  cannot  measure  a  contact-angle  with  any  accuracy  and 
because  the  actual  existence  of  a  contact-angle  is  a  matter  of  doubt.1 
The  problem  of  ore  flotation  is  a  very  simple  one  or  a  very  complex 
one,  depending  on  our  point  of  view.  It  has  been  customary  to  con- 
sider it  as  a  very  difficult  problem,  but  the  other  attitude  rather  ap- 
peals to  me.  There  is  nothing  strange  to  us  in  the  fact  that  water 
wets  glass  and  that  mercury  does  not.  We  also  know  that  water  does 
not  wet  greasy  glass  readily.  If  one  wishes  to  say  that  these  facts  are 
mysterious,  I  concede  it  willingly,  because  everything  becomes  mysteri- 
ous if  one  follows  it  back  far  enough.  All  I  claim  is  that  this  is  no 
more  mysterious  than  anything  else,  and  that  if  we  start  with  these 
bits  of  every-day  knowledge  as  given,  there  are  no  other  serious  diffi- 
culties in  connection  with  ore  flotation.  Ore  flotation  is  not  a  unique 
phenomenon,  it  is  merely  a  special  case  under  the  broad  heading  of 
emulsions. 

If  a  liquid  wets  a  solid,  it  is  adsorbed  by  the  solid,  forming  a  liquid 
film  on  the  surface  of  the  latter  and  displacing  the  air  film  that  was 
there.  If  a  liquid  is  not  adsorbed  by  the  solid,  it  does  not  wet  the 
solid.  The  formation  of  a  liquid  film  over  the  surface  of  a  wetted  solid 
accounts  for  the  experimental  fact  that  the  rise  of  a  liquid  in  a  capil- 
lary tube  is  independent  of  the  nature  of  the  walls  of  the  tube.  This 
has  always  seemed  a  very  improbable  state  of  things,  and  one  that 
could  be  justified  only  by  the  fact  that  it  was  so.  It  becomes  quite 
simple,  however,  the  moment  we  consider  that  the  rising  liquid  does 
not  come  in  contact  with  the  walls  of  the  capillary  tube  at  all.  We  are 
really  dealing  with  the  rise  of  liquid  in  a  liquid  tube,  and  it  makes  no 
difference  what  material  is  used  to  support  the  walls  of  the  liquid 
tube.  That  this  is  the  real  explanation  may  be  seen  from  the  fact  that 
concordant  results  are  not  obtained  when  a  liquid  is  allowed  to  rise  in 


*A  paper  read  at  the  joint  meeting  of  the  New  York  sections  of  the  Ameri- 
can Institute  of  Mining  Engineers  and  the  American  Electrochemical  Society 
on  May  12,  1916. 

iRayleigh,  Scientific  Papers  III,  354   (1902), 


ORE   FLOTATION  135 

a  dry  tube.     To  get  good  results  it  is  important  to  immerse  the  tube 
in  the  liquid  and  then  to  raise  the  tube. 

Since  the  wetting  of  a  solid  is  a  case  of  selective  adsorption,  we 
should  expect  that  one  liquid  would  wet  a  given  solid  more  readily 
than  another  liquid  does,  and  consequently  that  the  first  liquid  would 
displace  the  second  from  contact  with  the  solid.  No  systematic  study 
of  this  phenomenon  seems  to  have  been  made,  but  we  know  that  alcohol 
will  displace  oil  in  contact  with  metal2  and  that  water  will  displace 
kerosene  in  contact  with  quartz.3  If  we  shake  a  finely  divided  solid 
with  water  and  a  liquid  which  is  not  completely  miscible  with  water, 
an  oil  for  instance,  we  can  distinguish  three  cases.  The  solid  is  wetted 
entirely  by  water,  in  which  case  it  stays  in  the  water  phase  and  settles 
to  the  bottom  of  it.  The  solid  is  wetted  entirely  by  the  oil,  in  which 
case  it  stays  in  the  oil  phase  and  sinks  to  the  bottom  of  it.  The  solid 
is  wetted  simultaneously  by  oil  and  water,  in  which  case  it  passes 
into  the  interface  separating  the  two  liquids.  If  the  oil  is  less  dense 
than  the  water,  as  is  usually  the  case,  it  is  a  little  difficult  to  dis- 
tinguish between  the  last  two  cases.  If  the  non-aqueous  liquid  is 
denser  than  water,  chloroform  or  carbon  tetrachloride  for  instance,  it 
is  difficult  to  distinguish  between  the  first  and  third  cases.  The  par- 
ticles will  float  if  the  mean  density  of  solid  plus  adherent  oil  film  is 
less  than  that  of  the  water.  They  may  also  float  if  the  action  of 
gravity  is  not  sufficient  to  overcome  the  surface-tension  of  the  water 
and  thus  to  pull  them  through  the  surface.  The  maximum  weight  of 
substances  which  can  be  floated  can  be  calculated  from,  the  surface- 
tension  under  ideal  conditions.  This  calculation  applies  only  when 
the  solid  passes  into  the  upper  liquid,  and  does  not  hold  for  the  case 
where  the  solid  passes  into  the  interface. 

Since  we  are  dealing  with  selective  adsorption,  we  should  expect 
to  find  that  certain  substances  would  float  readily,  some  others  less 
well,  and  still  others  not  at  all,  both  the  nature  of  the  solid  and  of 
the  liquid  having  an  effect.  This  is  the  case  experimentally.  Hofmann 
found  that  lead  iodide,  silver  iodide,  mercuric  iodide,  mercuric  sul- 
phide, and  mercuric  oxide  were  floated  by  ether,  butyl  alcohol,  benzene, 
kerosene,  and  amyl  alcohol.  Copper  sulphide,  lead  sulphide,  and 
calcium  carbonate  were  floated  only  partially  by  ether,  but  com- 
pletely by  the  other  liquids ;  while  zinc  sulphide  and  tin  sulphide  did 
not  float  readily  in  ether  or  butyl  alcohol,  and  calcium  sulphate  was 
not  floated  by  any  of  the  liquids. 


sPockels,  Wied.  Ann.  LXVII,  669  (1899). 

3Cf.  Hofmann,  Zeit.  Pliys.  Ghem.  LXXXIII,  385   (1913). 


136  FLOTATION 

An  interesting  experiment,  which  has  been  done  in  my  laboratory,4 
is  to  shake  copper  powder  or  aluminum  powder  with  kerosene  and 
water.  The  metallic  powder  goes  into  the  kerosene  and  into  the  inter- 
face, producing  an  effect  of  molten  copper  or  molten  aluminum,  as 
the  case  may  be.  When  the  bottle  is  allowed  to  stand  after  having 
been  shaken,  the  metallic  powder  in  the  interface  creeps  up  the  side 
of  the  bottle  above  the  surface  of  the  liquid,  rising  higher  if  a  little 
alcohol  has  been  added.  I  have  seen  an  apparently  coherent  metallic 
film  rise  three  inches  above  the  surface  of  the  upper  liquid  phase.  If 
too  much  copper  or  aluminum  be  added,  the  kerosene  cannot  hold  all  of 
it  up  and  a  portion  falls  to  the  bottom  of  the  flask,  carrying  drops  of 
kerosene  with  it.  If  the  mixture  be  poured  out  on  a  piece  of  wood, 
the  copper  spreads  over  the  surface  of  the  wood  just  as  it  did  over 
the  surface  of  the  glass.  This  experiment  illustrates  the  principle  in- 
volved in  all  bronzing  liquids.  A  bronzing  liquid  consists  of  a  volatile 
liquid  which  will  hold  up  the  metal,  and  some  substance  which  will 
keep  the  metallic  powder  from  rubbing  off  too  readily  after  it  has 
been  applied.  The  aluminum  and  copper  powders  on  the  market  are 
coated  with  stearin.  This  makes  them  difficult  to  wet  with  water,  but 
special  experiments  have  shown  that  the  behavior  of  copper  or  alum- 
inum with  kerosene  is  qualitatively  the  same  whether  the  stearin 
coating  is  removed  with  ether  or  not. 

Similar  results  can  be  obtained  with  colloidal  solutions.  Isobutyl 
alcohol5  was  added  to  a  colloidal  gold  solution  obtained  by  reducing 
gold  chloride  with  carbon  monoxide.  When  the  two  liquids  are 
shaken,  the  gold  forms  a  thin  film  at  the  interface.  This  film  is  violet- 
blue  to  blue-green  by  transmitted  light  and  golden  by  reflected  light. 
A  thin  water  film  forms  between  the  isobutyl  alcohol  and  the  glass, 
and  the  gold  concentrates  in  the  dineric  interface  thus  formed,  making 
the  alcohol  appear  uniformly  gold-plated.  With  ether  the  gold  film 
rises  high  above  the  level  of  the  two  liquids.  With  carbon  bisulphide 
the  adherent  film  of  gold  appears  blue.  When  the  carbon  bisulphide 
is  broken  into  drops  by  shaking,  each  drop  appears  blue.  When  a 
blue  gold  was  obtained  by  reducing  gold  chloride  with  phosphorus 
dissolved  in  ether,  the  gold  went  into  the  dineric  interface.  When  a 
brownish-red  gold  was  obtained  in  this  way,  it  remained  in  the  water 
phase  and  showed  no  tendency  to  pass  into  the  interface.  This  differ- 
ence is  undoubtedly  due  to  an  adsorption  of  something  at  the  surface 
of  the  gold,  because  Reinders  found  that  0.005%  gum  arabic  prevents 


4Bancroft,  Trans.  Am.  Electrochem.  Soc.  XXIII,  294  (1913). 
sReinders,  Zelt.  Kolloi&chemie  XIII,  235  (1913). 


ORE    FLOTATION  137 

colloidal  gold  from  passing  into  the  ether-water  interface.  With 
carbon  tetrachloride,  carbon  bisulphide,  or  benzene,  the  gold  goes  into 
the  interface  as  before,  but  the  gum  arabic  prevents  its  changing 
from  red  to  blue. 

Colloidal  arsenic  sulphide  goes  into  the  dineric  interface  with  amyl 
alcohol  or  isobutyl  alcohol,  but  stays  in  the  water  phase  when  carbon 
tetrachloride,  benzene,  or  ether  is  the  second  liquid.  India  ink  goes 
completely  into  the  interface  with  amyl  alcohol,  carbon  tetrachloride, 
or  benzene ;  it  goes  partly  into  the  interface  with  isobutyl  alcohol,  and 
stays  entirely  in  the  water  phase  when  ether  is  the  second  liquid. 

Winkelblech6  has  shown  that  mere  traces  of  gelatine  in  water  can 
be  detected  by  shaking  with  organic  liquids,  the  gelatine  concentrating 
at  the  interface  to  form  a  film.  "A  heavy  precipitate  was  obtained 
when  10  c.c.  of  a  solution  containing  0.234  gm.  gelatine  per  litre  was 
shaken  with  benzene.  Precipitates  were  also  obtained  -when  the 
gelatine  solution  was  diluted  ten-fold,  twenty-fold,  and  even  forty- 
fold,  provided  10  c.c.  solution  were  taken  for  the  test.  At  the  highest 
dilution  the  concentration  of  the  gelatine  was  0.06  gm.  per  litre,  and 
there  were  consequently  0.06  mg.  in  the  10"  c.c.  taken  for  the  test. 
This  seemed  to  be  about  the  limit  at  which  a  precipitation  could  be 
detected  definitely.  *  *  *  Some  other  colloids  behave  like  the  glue 
colloid  (glutin),  and  can  be  shaken  out  of  their  solutions.  Other 
hydrocarbons  are  also  effective,  so  that  the  phenomenon  seems  to  be  a 
general  one.  Precipitation  was  obtained  with  albumin,  water-soluble 
starch  and  soap,  as  well  as  with  resin  dissolved  in  very  dilute  caustic 
soda.  The  colloids  grouped  as  mucin  can  be  precipitated  from  urine 
and  the  proteins  from  beer.  It  is  worth  noting  that  tannin  can  be 
precipitated  but  not  gallic  acid. 

"The  hydrocarbons  which  can  be  used  are  :  kerosene,  liquid  par- 
affine,  benzene,  chloroform,  and  carbon  bisulphide  (in  addition  to  ben- 
zene). The  result  varies  from  case  to  case.  With  the  hydrocarbons 
which  are  lighter  than  water,  the  precipitate  floats  on  the  water ;  with 
the  denser  hydrocarbon  the  precipitate  is  below  the  water  layer.  The 
emulsions  which  form  seem  to  have  very  nearly  the  same  density  as 
the  organic  liquid  used.  It  is  not  possible  to  get  the  precipitation 
with  all  liquids  which  are  non-miscible  or  slightly  miscible  with  water. 
Experiments  with  ether  were  entirely  unsuccessful. 

"As  a  complement  to  the  action  of  hydrocarbons  on  aqueous  col- 
loidal solutions  it  was  found  that  fats  dissolved  in  hydrocarbons  or 
similar  liquids  can  be  precipitated  in  the  surface  film  by  shaking  with 


QZeit.  angew.  Chem.  XIX,  1953   (1906). 


138  FLOTATION 

water.  Precipitations  were  obtained  with  butter,  olive-oil,  lanolin, 
and  vaseline.  It  was  also  found  that  the  emulsions  of  heavy  hydro- 
carbons or  carbon  bisulphide  with  the  fats  of  low  specific  gravity  also 
accumulate  below  the  water  layer,  only  a  small  portion  being  carried 
to  the  surface  by  adhering  air  bubbles.  When  water  is  used  for  shak- 
ing out,  the  precipitation  is  very  slight.  With  a  slightly  alkaline 
solution  such  as  dilute  lime-water,  heavy  voluminous  precipitates  were 
obtained  while  a  transparent  layer  of  fat  is  obtained  when  a  slightly 
acid  solution  is  used.  With  concentrated  alkali  or  acid  solutions, 
viscous  emulsions  are  obtained  which  hold  fast  considerable  amounts 
of  solution." 

Winkelblech  patented  the  use  of  such  organic  liquids  as  kerosene 
for  clearing  sewage  by  shaking  out  the  colloidal  oxidizable  matter. 
The  method  was  not  a  success  commercially,  because  less  than  40% 
of  the  oxidizable  matter  was  removed.7 

Briggs8  has  shown  that  sodium  oleate  is  removed  from  solutions  of 
different  strengths  during  the  process  of  emulsifying  benzene,  and  that 
the  amount  of  this  removal  depends  upon  the  strength  of  the  soap 
solution  and  the  specific  surface  of  the  benzene  phase.  Rayleigh9 
has  observed  an  interesting  case  in  which  dust  goes  into  the  water 
layer.  "In  the  course  of  some  experiments  last  year,  in  illustration 
of  Sir  George  Stokes'  theory  of  ternary  mixtures,  I  had  prepared  an 
association10  of  water,  alcohol,  and  ether,  in  which  the  quantity  of 
alcohol  was  so  adjusted  that  the  tendency  to  divide  into  two  parts  was 
almost  lost.  As  it  was,  division  took  place,  after  shaking,  into  two 
nearly  equal  parts,  and  these  parts  were  of  almost  identical  composi- 
tion. On  placing  the  bottle  containing  the  liquids  in  the  concentrated 
light  from  an  arc  lamp,  I  was  struck  with  the  contrast  between  the 
appearance  of  the  two  parts.  The  lower,  more  aqueous,  layer  was 
charged  with  motes,  while  the  upper,  more  ethereal,  layer  was  almost 
perfectly  free  from  them.  Some  years  ago  I  had  attempted  the  elimi- 
nation of  motes  by  repeated  distillation  of  liquid  in  vacuum,  con- 
ducted without  actual  ebullition,  but  I  had  never  witnessed  as  the 
result  of  this  process  anything  so  clear  as  the  ethereal  mixture  above 
described. 

"The  observation  with  the  ternary  association,  which  happened 


7Biltz  and  Krohnke,  Zeit.  angew.  Chem.  XX,  883  (1907). 

»Jour.  Phys.  Chem.  XIX,  210  (1915). 

^Scientific  Papers,  III,  569  (1902). 

^Association  is  here  employed  as  a  general  term  denoting  the  juxta- 
position of  two  or  more  fluids.  Whether  the  result  is  a  mixture  depends  upon 
circumstances. 


ORE    FLOTATION  139 

to  be  the  first  examined,  is  interesting,  because  the  approximate  equal- 
ity of  the  liquids  suggests  that  the  explanation  has  nothing  directly 
to  do  with  gravitation.  But  the  presence  of  the  alcohol  is  not  neces- 
sary. Ether  and  water  alone  shaken  together  exhibit  the  same  phe- 
nomenon. It  would  appear  that  when  the  two  liquids  are  mixed 
together  in  a  finely  divided  condition,  the  motes  attach  themselves  by 
preference  to  the  more  aqueous  one  and  thus  when  separation  into  two 
distinct  layers  follows,  the  motes  are  all  to  be  found  below.11*  *  * 

"I  have  lately  endeavored  to  obtain  some  confirmation  of  the 
views  above  expressed  by  the  use  of  other  liquids.  It  would  evidently 
be  satisfactory  to  exhibit  the  selection  of  motes  by  the  upper,  instead 
of  by  the  lower,  layer.  Experiments  with  bisulphide  of  carbon  and 
water,  and  also  associations  of  these  two  bodies  with  alcohol,  which 
acts  as  a  solvent  to  both,  gave  no  definite  result,  perhaps  in  conse- 
quence of  a  tendency  to  the  formation  of  a  solid  pellicle  at  the  com- 
mon surfaces.  But  with  chloroform  and  water,  and  with  associations 
of  chloroform,  water  and  acetic  acid  (acting  as  a  common  solvent) 
the  experiment  succeeded.  The  motes  were  always  collected  in  the 
upper,  more  aqueous,  layer,  even  when  the  composition  of  the  two 
layers  into  which  the  liquid  separated  was  so  nearly  the  same  that  a 
few  additional  drops  of  acetic  acid  sufficed  to  prevent  separation 
altogether. ' ' 

The  reverse  case  appears  to  occur  with  white  lead.  J.  Cruick- 
shank  Smith12  says:  "During  recent  years  the  practice  has  been 
adopted,  largely  among  white-lead  corroders  who  grind  their  own 
white  lead  in  oil,  of  doing  away  with  the  final  drying  of  the  white-lead 
pulp  as  it  comes  from  the  washing  process,  and  grinding  or  beating 
up  the  pulp  (exhausted  of  water  until  the  proportion  of  the  latter  does 
not  exceed  about  20  per  cent)  with  a  suitable  quantity  of  refined  lin- 
seed oil.  This  process  depends  on  the  greater  surface  attraction  which 
white-lead  particles  offer  to  linseed  oil  than  to  water.  It  enables  con- 
siderable economies  to  be  effected  in  the  manufacture  of  ground  white 
lead,  and  it  eliminates  risk  of  lead  poisoning  during  one  of  the  most 
dangerous  parts  of  the  white-lead  manufacturing  process."  Not 
enough  oil  is  added  to  float  the  white  lead  and  consequently  the  white 
lead  carries  the  oil  down  with  it,13  leaving  the  water  as  upper  phase. 

That  the  adhesion  between  the  solid  and  the  liquid  may  be  very 


clearness  of  the  upper  layer,  after  a  mixture  of  ether  and  alcohol 
has  been  shaken  up  with  dust,  had  already  been  observed  and  explained,  much 
as  above,  by  Barus,  Amer.  Jour.  Sci.  (3)  XXXVII,  122  (1889). 
12'The  Manufacture  of  Paint,'  92  (1915). 

attention  was  first  called  to  this  by  T.  R.  Briggs. 


140  FLOTATION 

marked  is  shown  by  the  behavior  of  the  so-called  water  wings.  These 
consist  of  a  closely  woven  fabric  readily  permeable  to  air  when  dry. 
When  thoroughly  wetted,  the  film  of  water  is  strong  enough  to  permit 
of  the  wings  being  blown  up  enough  to  float  a  person  with  ease.  Though 
I  know  of  no  direct  experiments  on  the  subject,  it  seems  probable  that 
the  gas  pressure  in  some  sandstone  anticlines  may  result  from  the  oil 
being  displaced  by  water,  which  would  wet  the  porous  rock  more  read- 
ily than  does  the  oil. 

In  many  of  the  cases  where  oil  flotation  has  been  employed  we  have 
a  sulphide  ore,  which  is  much  more  readily  wetted  by  oil  than  by  water, 
in  the  presence  of  a  silicious  gangue,  which  is  much  more  readily  wet- 
ted by  water  than  by  oil.  Consequently  the  gangue  tends  to  stay  in 
the  water  phase  while  the  ore  is  carried  up  by  the  oil.  The  use  of  an 
acid  solution  is  natural,  because  oil  adsorbs  hydroxyl  ions,14  and  these 
latter  cut  down  the  adsorption  of  the  solid.  Nagel15  found  that  when 
precipitated  chromic  oxide  is  shaken  with  water  and  benzene,  it  goes 
into  the  dineric  interface,  but  is  precipitated  from  it  by  the  addition  of 
caustic  alkali.  Zinc  sulphide  is  also  precipitated  from  the  dineric  in- 
terface of  kerosene  and  water  by  addition  of  alkali.  I  am  aware  that 
modern  flotation  practice  is  tending  to  the  use  of  neutral  or  slightly 
alkaline  solutions,  but  in  such  cases  air  plays  an  important  part,  and 
the  use  of  mixed  oils  may  introduce  a  new  set  of  factors.  It  must  aiso 
be  remembered  that  acid  in  ore  flotation  does  not  act  because  of  a  re- 
placeable hydrogen  atom,  but  by  cutting  down  the  concentration  and 
consequently  the  adsorption  of  hydroxyl  ions.  If  calcium  ions,  for  in- 
stance, cut  down  the  adsorption  of  hydroxyl  ions  sufficiently,  calcium 
hydroxide  would  behave  like  an  acid,  so  far  as  ore  flotation  is  con- 
cerned, though  it  would  be  alkaline  to  litmus  paper.  Somewhat  simi- 
lar cases  are  known.  Under  electrical  stress  albumin  moves  to  the 
cathode  in  acid  solutions,  and  also  in  calcium  chloride  solutions.  The 
effect  is  not  a  question  of  acidity.  The  direction  in  which  the  albumin 
moves  depends  upon  the  charge  of  the  ion  adsorbed  in  excess.  The  hy- 
drogen cation  and  the  calcium  cation  are  each  adsorbed  more  than  the 
chlorine  anion,  and  consequently  the  albumin  moves  to  the  cathode 
in  these  two  solutions.  I  do  not  know  whether  anything  of  this  sort 
is  a  factor  in  modern  flotation  practice. 

Since  no  systematic  experiments  have  been  made  to  determine  the 
exact  effect  of  temperature,  we  do  not  know  to  what  extent  the  appar- 
ent advantages  of  a  heated  solution  are  due  to  a  relative  change  in  the 


i^Twomey,  Jour.  Phys.  Chem.  XIX,  360  (1915). 
is Jour.  Phys.  Chem.  XIX,  570  (1915).       N 


ORE    FLOTATION  141 

selective  adsorption,  to  a  change  in  the  relative  densities  of  the  two  liq- 
uids, or  to  a  change  in  the  viscosities.  It  seems  probable  that  all  three 
changes  are  factors,  but  that  the  change  in  the  selective  adsorption  is 
the  important  one.  Of  course,  the  absolute  adsorption  must  decrease 
with  rising  temperature,  but  the  selective  adsorption  may,  and  prob- 
ably does,  increase  with  rising  temperature.  At  still  higher  tempera- 
tures the  decrease  in  absolute  adsorption  becomes  too  serious  and  there 
is  therefore  a  maximum  temperature  which  is  not  necessarily  the  same 
under  varying  conditions. 

We  now  have  to  consider  the  part  played  by  air  in  flotation.  Since 
the  density  of  air  is  low,  it  is  clear  that  a  film  of  adsorbed  air  or  an  at- 
tached bubble  of  air  will  be  very  effective  in  floating  a  solid  particle. 
If  we  like,  we  may  consider  air  as  an  extreme  case  of  a  second  liquid 
phase,  in  which  case  we  may  have  the  solid  remaining  in  the  air  phase 
under  suitable  conditions,  concentrating  in  the  interface,  or  remaining 
in  the  water  phase.  If  a  piece  of  metal  covered  with  an  air  film  be 
laid  very  carefully  on  the  surface  of  water,  the  water  may  wet  it  so 
slowly  that  the  metal  will  float  if  it  is  not  too  heavy.  If  the  surface  of 
a  copper  wire  be  converted  to  sulphide,  it  will  float  more  readily  be- 
cause the  adsorption  of  air  is  more  marked.  If  we  have  a  stearin  sur- 
face, as  in  the  case  of  copper  powder  or  aluminum  powder,  the  water 
has  still  less  tendency  to  wet  the  solid,  and  it  becomes  quite  difficult 
to  cause  the  commercial  copper  powder  or  aluminum  powder  to  sink 
in  water.  This  difference  in  readiness  to  wet  is  made  use  of  in  the  film 
flotation  processes  of  Wood  and  Macquisten. 

The  concentration  of  the  solid  at  the  interface  occurs  when  a  skin 
forms  over  the  surface  of  boiled  milk  or  of  cocoa  or  of  a  peptone  solu- 
tion. I  do  not  know  of  any  case  of  ore  flotation  analogous  to  this,  but 
doubtless  one  could  be  devised  if  anybody  was  interested  in  it.  In  the 
case  of  soap  solutions  we  have  a  partial  concentration  at  the  surface, 
but  the  bulk  of  the  soap  remains  distributed  through  the  water  phase. 
The  soap,  however,  adsorbs  so  much  air  that  boiling-point  determina- 
tions on  concentrated  solutions  are  worthless.16 

The  selective  adsorption  of  gases  and  vapors  by  solids  is  a  matter 
of  common  knowledge.17  The  film  of  condensed  gas  shows  itself  in  the 
abnormal  mobility  of  very  fine  powders,  in  the  fact  that  two  pieces  of  a 
broken  object  will  not  re-unite  when  pressed  together,  in  a  resistance  to 
the  passage  of  an  electric  spark  between  solid  terminals,  and  in  the 
behavior  of  the  crystal  detector  and  the  coherer  as  used  in  wireless  tel- 


and  Taylor,  Zeit.  phys.  Chem.  LXXVI,  182  (1911). 
^Bancroft,  Jour.  Phys.  Chem.  XX,  1   (1916). 


142  FLOTATION 

egraphy.  All  liquids  show  selective  adsorption  of  gases. and  vapors. 
The  most  striking  way  in  which  this  shows  itself  is  in  the  form  of  the 
splashes  when  a  drop  of  water,  5  mm.  in  diameter,  falls  on  a  sheet  of 
water  from  a  height  of  less  than  1  metre.  It  is  this  film  of  adsorbed 
gas  which  tends  to  prevent  the  coalescence  of  two  soap-bubbles  or  two 
impinging  jets  of  water  when  there  is  no  electrical  stress. 

Since  water  removes  air  more  or  less  quickly  from  practically  all 
minerals,  selective  flotation  from  already  wetted  ore  is  practically  im- 
possible, and  one  must  have  recourse  to  the  combined  effect  of  oil  and 
air.  It  so  happens  that  in  acid  or  neutral  solutions  air  seems  to  be  ad- 
sorbed by  organic  liquids  much  more  readily  than  by  water.18  Into 
100  c.c.  approximately  normal  caustic  potash  solution  0.5  c.c.  chloro- 
form was  dropped  from  a  5  c.c.  pipette.  The  chloroform  did  not  seem 
to  spread  out  on  the  surface  before  sinking  so  much  as  it  did  with 
water.  The  globules  sank  to  the  bottom  and  flattened  out ;  they  were 
distinctly  not  very  mobile,  and  seemed  to  sink  to  the  bottom  of  the  ves- 
sel. When  the  chloroform  was  dropped  into  the  water  it  broke  up  into 
a  number  of  drops  which  did  not  agglomerate  so  easily  as  in  the  water 
solution.  In  fact,  quite  a  little  shaking  was  necessary  in  order  to  make 
them  coalesce.  At  first  no  air  bubbles  could  be  detected,  but  after 
standing  for  five  minutes  a  very  small  bubble  appeared  on  the  chloro- 
form. Sulphuric  acid  was  then  added  until  the  solution  became  acid. 
The  flattened  drop  of  chloroform  at  once  assumed  the  shape  of  a  round 
ball  and  became  mobile.  An  air  bubble  also  appeared  in  the  centre 
of  the  drop. 

"Into  100  c.c.  approximately  normal  sulphuric  acid  solution  0.5 
c.c.  chloroform  was  dropped  as  before.  The  chloroform  spread  all  over 
the  surface  and  then  sank  through  the  solution  in  small  drops,  forming 
round  globules  with  air  bubbles  clinging  to  each.  It  was  hard  to  get 
rid  of  the  bubbles  on  the  chloroform  drops  by  shaking;  as  soon  as  one 
was  driven  off  another  bubble  appeared  exactly  in  the  centre  of  the 
drop.  When  the  bubbles  were  dislodged  from  the  drops,  they  rose  to 
the  surface  carrying  with  them  some  chloroform,  a  part  of  which  re- 
mained on  the  surface  until  it  evaporated,  while  the  rest  sank  back 
to  the  bottom  of  the  solution.  The  globules  were  very  mobile  and  coa- 
lesced readily.  Caustic  potash  was  added  to  the  solution,  making  it  al- 
kaline. The  chloroform  globule  flattened  immediately  and  the  air  bub- 
ble in  the  centre  disappeared.  In  still  another  experiment  an  acid  so- 
lution was  made  alkaline,  then  acid,  and  then  alkaline  again.  The  re- 


isTwomey,  Jour.  Phys.  Chem.  XIX,  360  (1915) 


ORE    FLOTATION  143 

suit  confirmed  Wilson 's  experiments,19  for  the  drop  of  chloroform  was 
always  flat  in  the  alkaline  solution  and  always  round  in  the  acid  solu- 
tion. There  is  scarcely  any  difference  to  be  noted  between  the  shape 
of  the  drop  in  acid  solution  and  in  pure  water.  The  same  results 
were  obtained  when  NaOH  and  HC1  were  substituted  for  KOH  and 
H2S04. 

"In  one  experiment  in  a  nitric-acid  solution  the  temperature  was 
raised  to  about  40°  C.  Bubbles  seemed  to  shoot  from  all  parts  of 
the  solution  to  the  chloroform  drop.  When  they  had  formed  a  large 
bubble  in  the  centre  of  the  chloroform,  the  air  bubble  rose  to  the  sur- 
face of  the  solution  as  in  the  other  cases. ' ' 

Of  course,  it  does  not  follow  that  the  relative  adsorption  of  gas  is 
always  greater  for  oil  in  acid  solution,  but  merely  that  this  seems  to 
be  true  in  the  cases  hitherto  studied.  It  is  purely  an  empirical  obser- 
vation. Another  interesting  fact  is  the  difficulty  that  is  experienced  in 
getting  air  bubbles  to  attach  themselves  in  some  cases  to  the  oil  films 
surrounding  the  solid  particles.  Some  people  have  even  claimed  that 
nascent  gas  is  essential,  but  this  is  absurd.  If  the  air  bubble  comes  in 
contact  with  the  oil  it  will  adhere ;  but  it  is  not  easy  to  bring  about  this 
contact.  It  can  be  done  by  vigorous  agitation  or  by  causing  dissolved 
gas  to  come  out  of  solution,  but  the  essential  thing  is  merely  to  bring 
the  gas  in  actual  contact  with  the  oil.  .  .  . 

Anderson20  classifies  flotation-oils  as  "frothing"  and  "collect- 
ing" oils.21  "There  is  at  times  some  difficulty  in  grasping  the  dis- 
tinction between  frothers  and  collectors  as  such,  for  one  oil  in  itself 
may,  and  often  does,  possess  both  frothing  and  collecting  properties. 
The  action  of  a  frothing  oil  is  such  as  to  produce  froth  in  greater  or 
less  amount,  dependent  on  the  frothing  power  of  the  oil.  A  collecting 
oil  has  a  collecting  power  for  sulphides  in  preponderance  over  its 
frothing  action,  being  therefore,  so  to  speak,  a  poor  f rother ;  a  collect- 
ing oil  may  have  simply  a  collecting  action  and  little  or  no  frothing  ac- 
tion. As  stated  in  the  foregoing,  some  oils  combine  both  the  proper- 
ties of  frothing  and  collecting  in  variable  degrees  of  each. 

"The  most  successful  frothing  oils  include  the  pine-oils,  cresylic 
acid  and  turpentines,  and  other  pyroligneous  products  from  the  distil- 
lation of  wood — notably  methyl  alcohol.22  The  coal-tar  phenols  and 
their  near  derivatives,  and  almost  all  of  the  so-called  essential  oils  are 


,  Jour.  Chem.  Soc.  I,  174  (1848). 
.  &  Chem.  Eng.  XIV,  136  (1916). 
21Van  Arsdale  calls  them  "foamers"  and  "oilers." 
t.  &  Chem.  Eng.  XIV,  136  (1916). 


144  FLOTATION 

good  frothers.  The  essential  oil  of  eucalyptus  finds  favor,  particularly 
in  Australian  practice,  on  account  of  relatively  low  cost  and  immediate 
supply.  Castor-oil,  to  which  reference  has  already  been  made,  when 
mixed  1 :  4  with  kerosene  has  found  application.  The  more  volatile 
products  of  petroleum,  including  kerosene  and  gasoline  [  ?],  have  been 
successful  frothing  oils. 

' '  So-called  mineral-oils  and  tar-oils  do  not  generally  form  good  no- 
tation froth,  but  have  a  marked  selective  action  on  the  sulphide  min- 
erals. Among  the  mineral  oils  are  included  the  following :  asphaltum 
base,  crude  petroleum,  refined  oil,  gasoline,  burning  oil,  cresol,  and 
coal-tar  creosotes. 

*  *  It  is  found  that  thick  oils  tend  to  form  viscous  coherent  flotation 
concentrates,  while  thin  oils  form  less  coherent  masses.  The  action  of 
coal-tar  in  stiffening  a  weak  ephemeral  froth  is  indicative  of  the 
former.  In  general  the  essential  oils  give  a  coherent  froth  and  satis- 
factory extraction;  oils  like  oleic  acid  or  candle-maker's  red  oil,  petrol- 
eum, and  lubricating  and  engine  oils  have  a  strong  tendency  to  produce 
heavy  thick  granules  which  will  not  float.  Oleic  acid  has  a  well- 
marked  power  to  float  silicates. "... 

Since  we  are  dealing  with  selective  adsorption,  we  should  ex- 
pect to  find  that  some  oils  would  be  better  than  others  for  certain  pur- 
poses. 

Anderson23  states  that  "oils  derived  from  the  destructive  distilla- 
tion of  wood,  such  as  wood-creosotes,  pyroligneous  acid,  and  the  like, 
are  found  to  give  the  best  recovery  on  galena  and  zinciferous  material ; 
coal-tar  products  are  better  adapted  to  the  successful  flotation  of  cop- 
per-bearing minerals."  There  are  no  independent  data  from  which 
this  result  could  have  been  predicted. 

Since  flotation  is  due  to  selective  adsorption,  anything  which  will 
change  the  latter  will  change  the  degree  and  nature  of  flotation  as  far 
as  the  oil-water  flotation  is  concerned.  Adding  a  third  liquid  which  is 
miscible  with  the  other  two  will  tend  to  make  the  oil  and  water  lay- 
ers more  nearly  alike  in  composition  and  therefore  in  properties.  This 
gives  us  a  possibility  of  varying  the  selective  adsorption  within  certain 
limits  and  its  possiblities  should  be  determined,  even  though  there 

may  be  no  economic  advantages In  some  experiments  recently 

made  at  Cornell  by  Mr.  Briggs,  it  has  been  found  that  addition  of  salt 
made  it  easier  to  shake  out  colloidal  ferric  oxide  with  benzene.  The 
reason  for  this  seems  to  be  that  the  salt  makes  the  colloidal  solution 
less  stable.  Any  substance  which  prevents  peptization  in  the  water 


.  <£•  Chem.  Eng.  XIV,  136  (1916). 


ORE    FLOTATION  145 

phase  or  promotes  it  in  the  oil  phase  will  tend  to  increase  the  flotation. 
I  do  not  yet  know  to  what  extent  this  is  applicable  to  ore  flotation ;  but 
Anderson24  reports  that  experiments  performed  on  a  60-mesh  product 
from  the  Joplin  district  containing  pyrite  and  galena  in  a  calcareous 
gangue  showed:  that  potassium  bichromate  will  deaden  galena  and 
permit  the  flotation  of  the  pyrite;  that  sodium,  potassium,  and  ferric 
sulphates  promoted  the  production  of  clean  concentrates ;  and  that  fer- 
rous sulphate  and  cupric  sulphate  were  very  harmful  to  the  successful 
flotation  of  this  particular  product,  flotation  being  practically  impos- 
sible in  their  presence.  Anderson,  of  course,  ventures  no  opinion  as  to 
why  these  salts  act  in  this  way ;  but  it  ought  not  to  be  difficult  to  work 
out  a  hypothesis  if  some  data  were  forthcoming.  The  inadequacy  of 
the  present  data  is  made  clear  by  the  statement  of  R.  H.  Richards 
that  in  the  case  of  a  certain  Tennessee  zinc  ore  the  addition  of  a  small 
amount  of  copper  sulphate  was  necssary  in  order  to  bring  about  suc- 
cessful flotation.  We  have  not  yet  made  any  experiments  on  the  fac- 
tors affecting  the  air-flotation  when  the  oil  is  reduced  to  a  minimum,  so 
I  will  not  discuss  that  point  at  all. 

There  seems  to  be  no  reason  to  suppose  that  ore-flotation  has  yet 
gone  beyond  the  first  stages  of  its  development,  and  certainly  a  clear 
knowledge  of  the  general  theory  should  be  a  help  in  promoting  the  de- 
velopment. 


t.  d-  Chem.  Eng.  XIV,  137  (1916). 


146  FLOTATION 


THE  THEORY  OF  FLOTATION 

BY  H.  HARDY  SMITH 
(From  the  Mining  and  Scientific  Press  of  July  1,  1916) 

It  appears  to  me  that  the  problem  of  elucidating  the  theory  of  flota- 
tion could  be  greatly  simplified  by  formulating  some  definite  line  of  at- 
tack; the  first  consideration  in  which  should  be  to  segregate  the  various 
physical  forces  with  their  attendant  phenomena,  and  to  attack  each  in 
turn. 

It  is  quite  possible,  in  fact,  most  probable,  that  some  of  the  forces 
come  into  play  in  all  the  phenomena,  but  by  delivering  a  massed  attack 
on  each  section  in  turn,  perhaps  success  can  be  achieved  more  easily. 

I  suggest  the  following  as  a  possible  segregation : 

(1)  The  physical  forces  governing  the  formation  of  bubbles  in 
a  pulp. 

(2)  The  physical  forces  governing  the  attachment  of  bubbles  to 
sulphide  particles  in  a  pulp. 

(3)  The  physical  forces  governing  the  stability  of  the  bubble  at- 
tachment. 

(4)  The  physical  forces  governing  the  stability  of  a  bubble  at  the 
free  surface  of  the  pulp. 

Leaving  out  of  consideration  those  processes  in  which  bubbles  are 
formed  in  a  pulp  by  the  chemical  action  of  one  substance  on  another, 
and  also  Mr.  Norris's  unique  process,  in  which  minute  bubbles  are 
'born'  in  a  pulp  which  is  super-saturated  with  a  gas,  and  regarding 
only  those  processes  in  which  a  gas  is  introduced  directly  from  an  ex- 
ternal source,  segration  No.  1  will  be  found  to  present  a  considerable 
problem. 

Several  of  your  correspondents  appear  to  be  laboring  under  the  de- 
lusion that  it  is  simply  necessary  to  introduce  air  violently  into  a  pulp 
either  by  agitation  or  blowing,  and  immediately  bubbles  of  the  right 
number  and  kind  obligingly  form  themselves.  Anybody  who  has  had 
practical  experience  with  flotation,  especially  with  the  so-called  air- 
froth  flotation,  knows  that  most  unfortunately  this  is  not  the  case.  No 
amount  of  agitation  or  blowing  will  produce  bubbles  of  the  right  kind 
and  number  in  absolutely  pure  water.  A  contaminating  agent  is  nec- 
essary, and  as  some  of  the  contaminating  agents  commonly  used  hap- 
pen to  be  oils,  concentration  by  frothing  most  unhappily  has  been 


THE   THEORY  OP    FLOTATION  147 

named  'oil-flotation,'  thereby  masking  the  real  significance  of  the  use 
of  the  reagent.  The  action  of  certain  substances  in  producing  innum- 
erable minute  bubbles  when  air  is  introduced  forcibly  into  a  pulp, 
seems  to  be  of  fundamental  importance,  since  without  these  bubbles  the 
most  common  forms  of  froth  flotation  cannot  be  considered. 

Professor  Pollock  of  Sydney  University,  in  Australia,  has  done 
some  very  interesting  and  useful  work  on  this  all-important  subject, 
and  I  believe  has  formulated  a  theory.  I  once  saw  a  set  of  instantan- 
eous consecutive  photographs  of  bubbles,  taken  by  him,  showing  their 
formation  after  the  introduction  of  a  blast  of  air.  With  pure  water  the 
bubbles  were  mostly  large,  and  even  the  small  ones  which  were  instan- 
taneously produced  had  a  tendency  to  collect  together  to  form  large 
ones.  With  contaminated  water  the  reverse  was  the  case,  the  instan- 
taneously produced  large  bubbles  seeming  to  break  down  into  smaller 
sizes. 

From  my  experience  in  the  practical  application  of  the  froth-flota- 
tion process,  I  am  inclined  to  believe  that  many  of  the  troubles  that 
crop  up  from  time  to  time  at  flotation  plants  are  due  to  the  inability 
of  the  reagent  used  to  produce  the  required  quantity  of  bubbles,  ow- 
ing to  the  appearance  of  some  reactive  substance  in  the  pulp.  Hence 
practical,  as  well  as  theoretical,  considerations  demand  a  thorough  un- 
derstanding of  the  physical  forces  governing  the  production  of  bubbles 
in  a  pulp. 

Coming  now  to  segregation  No.  2.  More  attention  has  been  paid  to 
this  phase  of  the  question  perhaps  than  to  any  other,  and  rightly  so, 
as  it  is  of  the  utmost  importance  in  all  flotation  processes,  those  em- 
ploying the  surface-film  effect  being  excepted.  Many  writers  pass 
lightly  over  the  problem  and  simply  state  that  the  bubbles  attach  them- 
selves preferentially  to  the  oil  or  gas-filmed  sulphide  particles. 

Let  us  now  see  whether  this  is  possible  if  the  two  forces  of  surface- 
tension  and  adhesion  are  alone  considered.  In  the  following  discourse 
surface-tension  can  be  most  simply  defined  as  that  force  acting  at  the 
surface  of  all  liquids  which  continually  tends  to  reduce  the  surface 
area;  and  adhesion  as  that  force  which  acts  across  the  interface  be- 
tween two  substances,  which  are  in  infinitely  close  contact,  and  tends 
to  keep  them  from  separating. 

Consider  a  particle  of  sulphide  mineral  (which,  for  the  sake  of 
clearness,  we  may  assume  to  be  nearly  spherical)  and  a  bubble  in  close 
contact,  in  the  interior  of  a  pulp,  but  before  the  bubble  has  actually 
'picked  up'  the  mineral.  (Fig.  1.)  Even  if  the  particle  possesses  ap- 
preciable adhesion  for  the  water,  the  surface  of  the  liquid  in  contact 


148 


FLOTATION 


with  the  particle  must  be  considered  as  tending  to  have  surface-tension, 
although  the  tendency  is  opposed  by  the  adhesion.  (See  T.  J.  Hoover's 
'  Concentrating  Ores  by  Flotation/  pages  50  to  55). 

In  the  first  case,  assume  the  adhesion  to  be  negligible.  The  surface- 
tension  forces  that  now  come  into  play  are  shown  in  Fig.  1,  where  Tg 
is  the  gas-liquid,  and  Ts  is  the  solid-liquid  surface-tension.  A  glance 


Fig.  I. 


Bubble  unattached 

Bubble- Film  continuous  and 

Bubble  perfectly  mobile. 


Bubble  attached  and 
Bubble- Film  discontinuous. 


at  the  force  diagram  will  show  that  whatever  the  value  and  direction 
of  the  forces  Ts  and  Tgy  their  component  Tc  can  never  be  greater 
than  Tg-\-Ts.  Therefore  surface-tension  alone  cannot  rupture  the  in- 
tervening film,  and  cause  the  bubble  to  envelop  the  particle.  If  the 
particle  possesses  appreciable  adhesion  vfor  the  liquid,  then  the  case 


THE    THEORY    OF    FLOTATION  149 

is  more  hopeless  still,  as  Tc  must  then  be  sufficiently  strong  to  rupture 
the  intervening  film  and  also  to  tear  it  away  against  the  action  of  the 
adhesive  force  between  the  solid  and  the  film. 

Once  a  rupture  has  been  effected,  bubble  attachment  resolves  itself 
into  a  struggle  between  surface-tension  and  adhesion,  the  former 
strongly  favoring  a  strategical  retirement  to  the  rear,  from  the  salient, 
so  as  to  straighten  the  line,  and  adhesion  endeavoring  to  hold  the  right 
wing  to  its  position. 

As  it  is  an  established  fact  (see  Fig.  2)  (Mr.  C.  T.  Durell  notwith- 
standing) that  a  bubble  contiguous  to  a  surface  with  negligible  adhe- 
sion does  become  attached  almost  immediately,  so  that  its  film  forms 
part  of  a  continuous  film  covering  both  solid  and  gas,  there  must  be 
some  force  that  causes  rupture  of  the  bubble-film  at  the  point  of  con- 
tact. 

In  the  case  of  two  plain  bubbles  in  pure  water  with  their  films  in 
contact,  the  immediate  coalescing  can  probably  be  explained  by  the  dif- 
ference in  vapor-pressure  existing  in  bubbles  of  different  radii.  But 
we  add  a  contaminating  agent  for  the  very  purpose  of  counteracting 
this  force  due  to  the  difference  in  vapor-pressure  so  as  to  allow  small 
bubbles  to  exist  in  the  presence  ol  larger  ones ;  otherwise  a  froth  would 
be  an  impossibility.  Hence  some  force  other  than  the  difference  in 
vapor-pressure  must  be  present  when  one  of  the  bubbles  happens  to 
have  some,  or  all,  of  its  interior  space  occupied  by  a  sulphide  particle. 

In  all  probability  this  additional  force  manifests  itself  in  the  phe- 
nomenon known  as  the  *  hysteresis '  of  the  contact-angle.  Hysteresis  is 
defined  as  the  lagging  of  effect  behind  cause,  and  a  contact-angle  is 
the  "effect"  that  is  "caused"  by  bringing  a  solid  surface  in  contact 
with  a  liquid  surface  in  the  presence  of  a  gas.  With  many  substances 
the  "effect"  (the  contact-angle)  does  not  assume  its  full  value  imme- 
diately, but  lags  behind.  The  reason  why  the  angle  changes  can  be 
fairly  well  explained  if  we  assume  that  there  is  a  force  acting  between 
a  solid  surface  and  a  gas,  tending  to  concentrate  the  gas  on  the  solid 
surface ;  and  that  this  force  is  strong  enough  to  act  across  a  thin  film 
of  the  liquid. 

In  Fig.  3  the  solid  is  a  piece  of  glass,  which  is  clean,  and  has  been 
immersed  for  some  time  in  the  liquid.  On  drawing  it  through  the  sur- 
face, a  contact-angle  is  immediately  formed,  and  for  any  given  angle, 
the  forces  Tsg,  Tig,  and  Ad  are  in  equilibrium  (ignoring  gravity).  If 
now  the  solid  possesses  the  power  to  adsorb  the  gas  through  the  very 
thin  film  at  the  toe  of  the  angle,  the  adhesion  of  the  liquid  for  the  glass 
will  be  lessened  and  a  corresponding  surface-tension  Tsl  set  up  in  the 


150 


FLOTATION 


direction  shown.  This  additional  force  will  be  sufficient  to  upset  the 
state  of  equilibrium,  the  toe  of  the  angle  will  recede,  and  the  angle  will 
increase  in  size.  The  stable  angle  will  be  reached  when  Tsg,  Tig,  Tls, 
and  Ad  have  such  magnitude  and  direction  as  to  balance  one  another. 

It  has  been  found  that  those  substances  which  possess  the  greatest 
power  to  vary  the  contact-angle  also  show  the  strongest  tendency  to 
float  under  suitabler  conditions,  and  it  is  reasonable  therefore  to  assume 
that  this  power  has  something  to  do  with  the  attachment  of  bubbles. 

The  problem  presented  by  segregation  (3)  is  not  nearly  so  formid- 


Fig.  3. 


Clean 
Glass. 


£/.. 


Fig-  4. 


Contact 
\:  Angle., 


Contact  Angle. 

"' 


able  as  that  just  considered;  it,  as  already  stated,  merely  resolves  it- 
self into  a  struggle  between  surface-tension  and  adhesion.  With  most 
substances  in  their  natural  state,  adhesion  is  altogether  too  strong, 
and,  even  if  the  film  at  the  point  of  contact  is  ruptured,  the  bubble  can- 
not attach  itself  on  account  of  the  inability  of  the  surface-tension  to 
tear  the  solid  and  the  liquid  surfaces  apart.  Hence  either  the  surface- 


THE    THEORY    OF   FLOTATION 


151 


tension  must  be  increased  or  the  adhesion  decreased.  The  latter  course 
is  usually  adopted,  as,  with  dilute  solutions,  the  former  is  difficult; 
and  except  for  very  small  amounts  is  an  impossibility. 

Although  an  absolute  increase  in  the  surface-tension  is  out  of  the 
question,  a  relative  increase  is  possible  by  raising  the  temperature. 
Both  surface-tension  and  adhesion  decrease  with  a  rising  tempera- 
ture, but  the  latter  much  faster  than  the  former ;  one  being  zero  at  the 
critical  temperature  and  the  other  probably  zero  at  the  boiling-point. 
This  is  one  of  the  reasons  why  solids  that  will  not  collect  bubbles  at  or- 
dinary temperatures,  will  do  so  when  the  boiling-point  is  approached. 

The  usual  methods  employed  for  decreasing  the  natural  adhesive- 
ness of  liquids  for  solids  are : 

(a)  To  allow  the  solid  to  take  on  a  film  of  gas  by  adsorption  (or 
occlusion  ? ) . 

(b)  To  allow  the  solid  to  take  on  a  film  of  oil  or  other  greasy 
matter  by  adhesion. 

(c)  A  combination  of  both  (a)  and  (b). 


A  B 

While  collecting  evidence  for  one  of  the  patent  lawsuits  that  are 
ever  with  us,  an  interesting  discovery  was  made.  A  piece  of  Broken 
Hill  sulphide  ore,  taken  from  the  centre  of  a  large  uncracked  block, 
was  found  to  contain  0.0037%  of  natural  grease,  as  obtained  by  an 
ether  extract.  Samples  were  taken  from  several  other  mines,  and  all 
gave  an  oily  residue  after  extracting  with  ether  in  a  most  careful 
manner.  Perhaps  it  is  just  as  well  to  add  that  this  was  discovered 
accidentally  and  was  not  being  specially  sought  as  prospective  evi- 
dence. This  discovery  goes  a  long  way  toward  explaining  the  prefer- 
ential adhesion  of  bubbles  to  sulphide  particles. 

The  tenacity  with  which  the  bubble  holds  the  particle  depends  on 
the  length  of  the  line  of  contact,  which  in  turn  depends  on  the  size 
of  the  contact-angle,  itself  proportional  to  the  relative  values  of  sur- 
face-tension and  adhesion.  (See  Fig.  4.) 

If  the  adhesion  is  negligible,  and  the  particle  is  large  in  comparison 
with  the  bubble,  the  result  would  be  as  shown  in  Fig.  A. 


152  FLOTATION 

If  the  particle  is  small,  then  the  result  would  be  as  in  Fig.  B. 

As  adhesion  increases,  the  tendency  is  for  the  particle  to  get  more 
and  more  out  of  the  bubble  and  into  the  liquid  until  the  surface-tension 
does  not  act  over  a  sufficiently  long  line  of  contact  to  hold  the  weight  of 
the  particle,  and  it  falls  off. 

The  problem  presented  by  segregation  (4)  has  been  dealt  with  in  a 
most  excellent  manner  by  Mr.  W.  H.  Coghill  in  the  Mining  and  Scien- 
tific Press  of  February  26,  1916.  His  remarks  in  regard  to  a  lowering 
of  the  surface-tension  per  se  not  being  essential  to  the  formation  of  a 
froth  are  most  timely. 

The  tension  that  exists  in  a  pure  liquid  film  is  unlike  all  other  ten- 
sions with  which  we  are  familiar,  in  that  the  stress  is  not  proportional 
to  the  strain.  Within  the  elastic  limit  (that  is,  the  limit  wherein  the 
substance  will  return  to  its  original  shape  when  the  contorting  force 
is  removed)  a  steel  rod,  or,  taking  what  is  more  familiar  still,  a  steel 
spiral  spring,  needs  twice  the  pulling  force  to  stretch  it  twice  as  much, 
and  so  on.  The  Avell-known  spring  balance  depends  on  this  fact.  But 
with  a  liquid  film  the  same  force  can  continue  to  cause  an  extension 
until  rupture  takes  place,  in  spite  of  the  fact  that  the  film,  right  up  to 
the  point  of  rupture,  is  within  the  elastic  limit  according  to  the  above 
definition. 

It  is  plain  then  that  our  common  conception  of  a  tension  must 
be  entirely  revised  when  we  come  to  deal  with  the  tension  at  the  sur- 
face of  a  liquid.  For  a  system  to  be  in  a  state  of  stable  equilibrium  it 
must  offer  a  greater  resistance  to  any  force  which  tends  to  change  its 
configuration,  and  as  a  pure  liquid  film  does  not  fulfill  this  require- 
ment it  cannot  possess  stability. 

The  extreme  instability  of  bubble-films  is  strikingly  shown  by  the 
phenomenon  in  certain  boiling  liquids,  with  which  we  are  all  painfully 
familiar  in  our  student  days,  called  '  bumping. '  In  the  absence  of  nu- 
clei on  which  to  form,  the  radius  of  a  steam  bubble  when  it  first  comes 
into  being  must  be  infinitely  small,  and  the  vapor-pressure  to  balance 
the  surface-tension  of  these  small  bubbles  is  large.  Therefore  before 
the  bubbles  can  expand  and  rise  through  the  liquid  (that  is,  before  boil- 
ing can  occur)  the  temperature  must  be  raised  above  the  natural  boil- 
ing-point of  the  liquid.  As  soon  as  the  bubble  has  expanded  to  ap- 
preciable size,  the  vapor-pressure  of  the  liquid  is  in  excess  of  that  nec- 
essary to  balance  the  surface-tension,  and  the  bubble  expands  so  rap- 
idly that  it  literally  explodes. 

A  boiler  does  not  explode  until  its  steel  plates  are  actually  rup- 


THE    THEORY    OF   FLOTATION  153 

tured,  but  the  bubble  explodes  at  the  bottom  of  the  beaker,  that  is, 
while  its  shell  is  actually  in  existence. 

In  the  case  of  a  solid,  the  greater  the  tension  the  greater  the  tensile 
stress  developed;  for  a  material  of  given  strength,  the  greater  the 
tensile  stress,  the  greater  the  chance  of  rupture. 

This  line  of  reasoning  does  not  hold  in  the  case  of  a  liquid  film. 
The  idea  that  a  bubble  film  can  be  ruptured  by  the  force  of  its  own  sur- 
face-tension is  about  equivalent  to  the  idea  that  a  man  can  lift  himself 
by  his  own  shoe-strings. 

It  is  obvious  from  the  nature  of  the  molecular  forces  engaged,  that 
the  greater  the  surface-tension  the  greater  the  ultimate  tensile  strength 
of  the  film.  The  lowering  of  the  tension  in  itself  therefore  cannot  give 
greater  stability  to  a  liquid  film ;  but  the  surface  adsorption,  which  ac- 
companies the  lowering  of  the  tension  in  the  case  of  certain  solutes,  can. 

For  reasons  that  need  not  be  gone  into,  a  solute  which  lowers  the 
surface-tension  of  a  liquid,  concentrates  at  the  surface  of  the  solution, 
but  this  process  of  concentration  (called  adsorption)  takes  a  certain 
definite  time  to  reach  its  full  value.  Now,  if  a  film  of  the  solution  be 
stretched,  new  surface  is  produced,  and  this  new  surface  at  the  moment 
of  production  possesses  greater  tension  than  the  rest  of  the  surface,  be- 
cause the  surface  adsorption  has  not  had  time  to  reach  its  full  value. 
It  therefore  offers  a  greater  resistance  to  the  stretching  force,  and  ful- 
fills the  conditions  for  stable  equilibrium.  So  strong  is  the  adsorption 
factor  in  certain  cases,  that  practically  the  whole  of  the  solute  is  con- 
centrated in  the  surface  layers,  and  therefore,  although  the  absolute 
quantity  in  the  solution  may  be  exceedingly  slight,  the  surface  effect  it 
produces  is  considerable.  This  explains  the  efficacy  of  the  extremely 
small  amount  of  contaminating  agent  used  in  some  froth-flotation 
plants. 

In  a  mineral-froth,  it  is  strikingly  obvious  that  those  bubbles  which 
have  their  films  thickly  studded  with  sulphide  particles  have  their  sta- 
bility enormously  increased.  In  some  froths,  one  such  bubble  can  be 
seen  pursuing  the  even  tenor  of  its  way,  amid  a  regular  holocaust  of  its 
less  fortunate  brethren.  The  reason  for  this  is  not  quite  clear,  but  it  is 
probably  due  to  the  adhesive  force  between  the  liquid  and  the  solid. 

The  above  remarks  are  given  for  what  they  may  be  worth,  in  the 
hope  that  they  may  be  of  some  assistance  to  other  mill-men,  who,  like 
myself,  are  anxious  to  see  the  inner  workings  of  a  flotation  process 
clearly,  as  by  the  light  of  day,  but  at  present,  only  perceive  them  dimly, 
as  by  the  flicker  of  a  candle  at  the  far  side  of  a  50-ft.  stope. 


154  FLOTATION 


THE  FLOTATION  OF  MINERALS 

By  ROBERT  J.  ANDERSON 
(From  the  Mining  and  Scientific  Press  of  July  8,  1916) 

*Many  phenomena  are  supposed  to  contribute  to  the  flotation  of 
minerals,  whether  in  whole  or  in  part  is  a  mooted  question.  I  shall 
only  sketch  roughly  the  present  tendency  of  ideas  and  make  no  refer- 
ence to  the  first  early  and  crude  notions,  which  are  now  mainly  of  his- 
torical interest. 

SURFACE-TENSION  has  been  well  defined  in  articles  appearing  in  the 
Journal  of  the  American  Chemical  Society  during  the  years  from  1908 
to  1913.  The  theory  has  been  treated  in  particular  by  Laplace,  Gaus, 
and  more  recently  by  Van  der  Waals,  and  by  Willows  and  Hatschek.1 
As  defined  by  Jones,2  "potential  energy,  present  at  the  surface  of  liq- 
uids, produces  a  tension  which  is  known  as  surface-tension."  The  phe- 
nomena invariably  indicative  of  surface-tension  are  :  Drops  of  a  liquid 
not  exposed  to  an  external  force,  that  is,  either  suspended  in  another 
liquid  of  the  same  specific  gravity  or  freely  falling,  assume  a  spherical 
shape,  the  sphere  being  that  form  of  body  with  the  smallest  surface 
per  given  volume ;  further,  if  water  be  placed  in  an  open  vessel  its  sur- 
face film  will  be  a  measurable  quantity,  and  its  thickness  will  vary  with 
a  number  of  factors  of  which  temperature  is  one.  Its  thickness  is 
observed  as  ranging  from  4  X  10"5  cm.  to  4  X  10"8  cm.,  and  its  density, 
when  referred  to  the  main  bulk  of  the  water  below,  will  approximate 
2.14.  Surface-tension  is  not  affected  by  the  surface  area,  It  is 
numerical  in  value  and  expressed  in  dynes  per  centimetre.  It  is  a 
variable  factor  dependent  on  temperature,  increasing  numerically 
with  falling  temperature,  for  example,  water  at  18°  C.  has  a  surface- 
tension  of  73  dynes  per  centimetre,  and  at  0°  C.  this  increases  to  75 
dynes.  At  the  critical  temperature  of  a  liquid  its  surface-tension 
becomes  nil. 

All  liquids  have  a  definite  cohesion  or  tensile  strength,  which  is  as- 
cribed to  the  mutual  attraction  of  their  molecules.  This  then  is  com- 
parable to  a  pressure  existing  within  a  liquid,  which  has  been  termed 
the  '  intrinsic '  pressure.  Naturally  the  value  of  the  surface-tension  of 


*  Abstract  of  paper  read  at  the  Arizona  (September  1916)  meeting  of  th.e 
American  Institute  of  Mining  Engineers. 

i Willows  and  Hatschek:  'Surface  Tension  and  Surface  Energy,'  1915. 
2 Jones:   'Elements  of  Physical  Chemistry, \1907. 


THE    FLOTATION    OF    MINERALS  155 

solids  is  numerically  high.  The  surface-tension  of  a  pure  liquid 
against  its  vapor  is  markedly  affected  by  the  addition  of  soluble  con- 
taminants. Some  salts  will  raise  the  surface-tension  of  water  while 
others  will  lower  it ;  the  fact  that  the  salts  of  weak  acids  will  lower  the 
surface-tension  of  water  is  explained  by  the  fact  that  free  acid  is  lib- 
erated by  hydrolysis.  It  is  further  known  that  all  acids  will  lower  the 
surface-tension  of  water,  which  is  also  decreased  by  the  addition  of  oil, 
or,  in  other  words,  oil  will  reduce  the  interfacial  tension  between  the 
water-air  phases.  A  phenomenon  for  which  no  explanation  has  been 
given  is  the  one  showing  that  the  addition  of  contaminants  may  either 
raise  or  lower  the  surface-tension  of  water,  but  such  addition,  while  it 
may  decrease  that  tension  greatly,  can  increase  it  only  slightly.  Any 
lowering  of  surface-tension  is  more  marked  in  a  liquid  that  has  a 
high  surface-tension,  such  as  water,  than  in  liquids  of  low  surface-ten- 
sion. 

There  can  be,  of  course,  no  surface-tension  without  adsorption, 
which  produces,  in  the  case  of  positive  adsorption,  an  increased  sur- 
face concentration  resulting  from  a  lowering  of  the  surface-tension  by 
the  contaminating  and  dissolved  substance,  whatever  it  may  be.  The 
equation  of  Gibbs  (u  =  —  c/Rt.do/dc)  gives  the  relationship  between 
surface-tension  and  the  distribution  of  the  solute  between  the  bulk  of 
the  liquid  and  the  film  interface.  Here  the  notation  is : 

u  —  excess  of  substance  in  the  surface  layer, 

c  =  concentration  in  the  main  body  of  the  liquid, 

R  =  the  gas  constant, 

t  =  absolute  temperature, 

o  =  surface-tension. 

This  shows  that  when  the  surface-tension  is  reduced  by  the  addition  of 
a  contaminant,  the  quantity  do/dc  is  negative  and  u  is  positive  (from 
algebraic  consideration).  The  surface  film  then  contains  more  of  the 
contaminant  than  the  main  body  of  the  solution.  If  the  surface  film 
contains  less  of  the  contaminant  than  the  main  body  of  the  solution  it 
is  a  case  of  negative  adsorption. 

As  given  in  the  foregoing,  the  surface  of  a  liquid  against  its  vapor 
is  in  tension;  the  surface  of  liquid  against  another  liquid,  or  a  gas  or 
solid,  is  also  in  a  state  of  tension,  termed  interfacial  tension.  In  the 
flotation  machine  the  following  conditions  obtain :  Pulp  consisting  of 
ore  of  approximately  80-mesh,  water  in  ratio  of  3:1  of  ore,  and  oil 
in  disappearingly  small  amount,  is  being  violently  agitated.  For  the 
sake  of  a  specific  case,  the  air  is  being  forced  mechanically  into  the 
swirling  pulp  by  beaters  or  stirrers.  The  phases  present  in  flotation  by 


156  FLOTATION 

the  oil-froth  process  are  therefore:  solid-liquid  (ore-water),  solid-liq- 
uid (ore-oil)  solid-gas  (ore-air),  liquid-liquid  (water-oil),  liquid-gas 
(water-air),  and  liquid-gas  (oil-air).  Thus  six  tensions  are  present, 
but  if  the  oil  is  soluble  in  the  water  the  tensions  are  reduced  to  three. 
It  is  known  that  pure  water  cannot  be  made  to  maintain  a  persistent 
froth  because  its  surface-tension  is  too  high.  Acid,  if  present,  will 
lower  the  surface-tension  of  water,  as  will  oil,  if  it  is  soluble. 

Certain  metallic  sulphides,  such  as  galena,  have  the  power  of  float- 
ing on  undisturbed  water;  they  are  not  wetted  and  the  curve  of  contact 
is  convex.  Some  gangue  minerals,  such  as  quartz,  possess  an  adhesive 
force  of  attraction  for  water  that  exceeds  the  intrinsic  pressure  of  the 
water;  they  are  therefore  wetted  and  sink  to  the  bottom,  being  drawn 
through  the  surface  film.  Such  properties  of  the  minerals  are  affected 
by  the  presence  of  oil,  acid,  and  other  reagents.  Oil  has  a  greater  ad- 
hesive attraction  for  sulphide  minerals  than  for  gangue  minerals ;  and 
the  addition  of  acid  and  oil  (if  it  is  soluble)  acts  as  a  contaminant  that 
will  lower  the  surface-tension  of  the  water  and  aid  in  the  production 
of  a  persistent  froth.  Let  us  now  look  into  the  question  of  adsorption 
and  see  what  part  it  plays  in  flotation,  since  it  is  so  requisite  to  the 
production  of  a  variable  surface-tension. 

ADSORPTION.  Generally  speaking,  adsorption  deals  with  the  un- 
equal distribution  of  substances  at  the  interface  between  dissimilar 
phases  such  as,  solid-solid,  solid-liquid,  solid-gas,  liquid-liquid,  liquid- 
gas,  and  gas-gas.  It  is  purely  a  physical  effect.  Commonly,  adsorp- 
tion3 is  construed  to  be  the  result  of  the  condensation  of  a  disperse 
phase  upon  the  interfacial  boundary  solid-liquid.  Returning  for  a 
moment  to  the  Gibbs  equation  quoted  above,  adsorption  may  occur  if 
the  interfacial  tension  solid-liquid  is  reduced,  this  being  positive  ad- 
sorption. If,  however,  such  an  interfacial  tension  is  raised  in  value  it 
is  a  case  of  negative  adsorption,  as  the  solute  or  disperse  phase  will  be 
rejected  from  the  surface.  Any  condensation,  strictly  stated,  of  a  so- 
lute or  disperse  phase  in  the  interfacial  boundary  separating  liquid- 
liquid  or  liquid-vapor  is  held  to  be  a  special  case  of  adsorption.  How- 
ever, in  the  general  sense,  the  phenomenon  is  looked  upon  as  being  the 
result  of  condensation  of  a  disperse  phase  in  the  interface  of  two  im- 
miscible phases.  Adsorption  is  shown  strikingly  by  colloid  gels — the 
product  obtained  by  the  coagulation  of  sols — and  certain  cases  of  se- 
lective adsorption  are  most  remarkable.  Adsorption  will  naturally 
vary  with  the  surface  exposed.  In  Miss  Benson's  experiments  with 


sBriggs:  Jour.  Phys.  Chem.,  Vol.  XIX,  No.  3,  p.  210  (March  1915). 


THE  FLOTATION  OF  MINERALS  157 

ainyl  alcohol  in  aqueous  solution,  amyl  alcohol  reduced  the  surface- 
tension  of  the  water,  and  it  was  found  by  producing  a  voluminous 
froth  that  the  alcoholic  concentration  in  the  froth  exceeded  that  in 
the  bulk  of  the  aqueous  solution  by  about  5%.  A  froth  has  a  very 
large  surface,  and  it  would  be  expected  that  the  adsorption  would  be 
greater.  Such  experiments  prove  the  value,  qualitatively,  of  the  Gibbs 
rule. 

Recent  work  shows  that  all  solids  do  condense  gases  on  their  sur- 
faces and  retain  them  there  with  great  tenacity.  Liquids  in  like  man- 
ner adsorb  gases.  Further,  liquids  and  solids  exhibit  selective  adsorp- 
tion of  gases.  Although  this  selective  adsorption  obtains,  no  proof  has 
been  submitted  indicating  that  the  amount  of  gas  adsorbed  by  one  sub- 
stance is  largely  different  from  the  amount  adsorbed  by  another  sub- 
stance. An  electric  charge  on  an  adsorbed  substance  probably  would 
influence  the  amount  adsorbed.  The  adsorption  of  air  plays  an  import- 
ant role  in  flotation,  for,  as  Breuer  points  out,  the  adsorbed  air  film  is 
enormously  responsible  in  preventing  the  coalescence  of  solid  particles. 

A  comprehensive  study  of  the  adhesion  of  small  particles  of  solid 
to  the  dineric  interface  (surface  separating  two  liquid  phases)  has 
been  made  by  Hofmann4  based  on  the  theory  of  Des  Coudres.5  From 
the  standpoint  of  flotation  this  may  be  given  as  follows :  If  a  solid  par- 
ticle, such  as  quartz,  is  wetted  much  more  strongly  by  water  than  by 
another  liquid,  such  as  oil,  the  water  will  displace  the  oil,  and  a  film 
of  water  will  form  about  the  quartz  particle  according  to  the  relative 
forces  of  adhesion.  Then  the  quartz  particles  will  remain  in  the  water 
phase  if  the  water  has  a  specific  gravity  greater  than  the  oil,  regardless 
of  their  size ;  but  if  now  the  oil  has  a  greater  specific  gravity  than  the 
water,  then  the  quartz  particles  will  remain  in  the  water  phase  until 
the  size  of  the  particles  is  such  that  the  force  of  gravity  will  remove 
them  from  the  water.  Conversely,  if  a  solid  particle,  such  as  galena,  is 
wetted  more  strongly  by  oil  than  by  water,  the  oil  will  form  a  surface 
film  about  the  particle  and  hence  prohibit  the  particle  from  being  wet- 
ted by  water,  that  is,  from  entering  the  water  phase.  Then  the  galena 
wrill  only  enter  the  water  phase  when  the  water  is  more  dense  than 
the  oil,  and,  further,  when  the  galena  particles  are  of  such  a  size  that 
the  force  of  gravity  overcomes  the  adhesion  of  the  oil  film  to  the  oil. 

Returning  to  purely  theoretical  considerations,  Hofmann  draws 
certain  conclusions  that  deal  with  the  supposition  that  solid  particles 
will  then  remain  in  the  surface  separating  two  immiscible  liquids,  if 


*Zeit.  Phys.  Ghent.,  Vol.  LXXXIII,  p.  385,  1913. 
*Arch.  Entwicklungsmechanik,  Vol.  VII,  p.  325,  1898. 


158  FLOTATION 

those  particles  are  wetted  partly  by  each  liquid.  I  quote  Bancroft  at 
length  on  this  matter.6  "The  solid  particles  tend  to  go  into  the  water 
phase  if  they  adsorb  water  to  the  practical  exclusion  of  the  other 
liquid ;  they  tend  to  go  into  the  other  liquid  phase  if  they  tend  to  ad- 
sorb the  other  liquid  to  the  practical  exclusion  of  the  water ;  while  the 
particles  tend  to  go  into  the  dineric  interface  in  case  the  adsorption  of 
the  two  liquids  is  sufficiently  intense  to  increase  the  miscibility  of  the 
two  liquids  very  considerably  at  the  surface  between  solid  and  liquid. ' ' 

Any  simultaneous  adsorption  of  two  immiscible  liquids  by  a  solid 
would  tend  to  form  a  homogenous  liquid  phase  at  the  surface  of  the 
solid. 

In  regard  to  the  effect  of  contaminants  or  other  impurities  in  con- 
tact with  two  immiscible  liquids,  this  condition  obtains:  If  the  contam- 
inant is  soluble  in  one  liquid  but  not  in  the  other,  and  also  lowers  the 
interfacial  tension  of  the  two,  the  equation  set  forth  by  Gibbs  exacts 
the  requirement  that  the  contaminant  should  obtain  in  the  interface. 
Examples  of  this  prove  the  validity  of  the  law. 

The  terms  adsorption  and  absorption  have  been  used  interchange- 
ably in  some  writings,  thus  contributing  to  the  already  existing  confu- 
sion of  ideas. 

ABSORPTION  OR  OCCLUSION.  There  are  three  ways  by  which  gases 
can  be  held  with  reference  to  solids:  (1)  By  surface  adsorption ;  (2)  in 
solid  solution;  and,  (3)  by  occlusion.  The  term  'occlusion'  has  been 
applied  indiscriminately  to  any  of  these  methods  by  which  gases  are 
held  by  solids.  Strictly  speaking,  by  'occluded'  gas  is  meant  gas  that 
is  absorbed  and  held  in  finely-divided  pores  or  openings,  which  may  be 
of  microscopic  size.  A  recent  theory7  holds  that  occlusion  plays  the 
operative  role  in  the  flotation  of  minerals  by  all  processes.  I  am  un- 
able to  reconcile  myself  to  this  explanation,  for  a  number  of  reasons. 
Marked  instances  of  occlusion  at  normal  temperature  are  known  only 
in  certain  amorphous  substances,  like  charcoal.  Many  metals,  of 
course,  both  in  the  liquid  and  solid  states,  have  the  power  of  occlud- 
ing gases,  often  in  marked  degree.  There  may  be  and  undoubtedly  are 
fine  pores  in  the  floatable  minerals,  which  may  in  a  sense  be  considered 
as  an  assemblage  of  capillary  tubes ;  these  can  and  do  occlude  gas.  Yet 
occlusion  is  marked  only  in  amorphous  substances  and  in  certain  met- 
als as  just  stated.  It  is  definitely  known  that  occluded  gases  are  re- 


'••Bancroft:  Jour.  Phys.  Chem,,  Vol.  XIX,  No.  4,  p.  287  (April  1915). 
fDurell:  M.  &  S.  P.,  Vol.  CXI,  No.  12,  p.  428  (Sept.  18,  1915)  and  Durell 
Met.  d  Chem.  Eng.,  Vol.  XIV,  No.  5,  p.  251   (March  1,  1916). 


THE    FLOTATION    OF    MINERALS  159 

tained  with  great  tenacity  by  the  substances  occluding  them  and  there- 
fore are  expelled  only  with  difficulty.  It  seems  anomalous  to  hold  that 
the  occluded  gas  can  depart  from  the  mineral  occluding  it  with  suffi- 
cient speed  to  aid  the  air  bubbles  in  the  liquid  in  the  process  of  flota- 
tion. I  believe  firmly  that  occlusion  is  not  a  cogent  factor  in  flotation, 
and  that  a  more  consistent  theory  may  be  formulated  without  postulat- 
ing these  conjectures  regarding  occlusion. 

COLLOIDS,  in  the  original  definition  of  the  term  by  Thomas  Graham, 
do  not  constitute  a  definite  class  of  substances ;  a  large  number  of  dif- 
ferent substances  may  be  made  to  assume  the  colloidal  state  if  proper 
precautions  are  taken.  All  of  which  reveals  the  striking  fact  that  this 
colloidal  condition  is  a  state  and  not  a  form  of  matter.  The  ultra- 
microscope  of  R.  Zsigmondy  and  H.  Siedentopf  has  greatly  increased 
our  knowledge  of  colloids.  A  general  statement  may  be  made  regard- 
ing colloids:  that  they  do  not  show  osmotic  pressure  in  appreciable 
amount.  Colloidal  solutions — sols — are  regarded  as  systems  of  two 
phases,  in  which  the  dissolved  substance  is  the  disperse  phase  and  the 
solvent  the  continuous  phase. 

Since,  in  flotation,  the  ore  is  often  as  small  in  size  as  certain  of  the 
colloids,  the  pulp  (ore,  water,  etc.)  can  be  looked  upon  as  a  coarse  sus- 
pension, and  the  laws  of  colloids  apply  here  with  equal  force  as  in  the 
realm  of  colloidal  chemistry.  So-called  suspensions  are  systems  con- 
sisting of  solid  particles  of  microscopic  size  distributed  through  a 
liquid.  As  mentioned  by  Ralston,8  Reinders  has  treated  at  length 
the  particular  case  of  a  solid  phase  maintained  in  contact  with 
two  liquid  phases,  that  is,  two  immiscible  liquids.  His  work  is  based 
on  the  different  iiiterfacial  tensions  existing,  and  his  experiments 
and  those  of  Hofmann,  as  mentioned  in  an  earlier  paragraph,  have 
considerable  bearing  on  the  flotation  problem. 

EMULSIONS  are  fairly  coarse  dispersions  of  one  liquid  in  another 
with  which  it  is  immiscible.  The  simplest  and  commonest  emulsions 
are  the  pure-oil  water  emulsions,  containing  no  emulsifying  agent  such 
as  soap,  proteids,  etc.  In  such  systems  the  oil  globules  can  be  coagu- 
lated by  electrolytes,  they  show  the  Brownian  movement  strikingly, 
and  can  even  be  retained  by  some  filtering  media.  Any  process  of 
emulsification  is  dependent  on  a  lowering  of  surface-tension,  or,  to  be 
more  precise,  on  a  lowering  of  the  interfacial  tension  between  the  two 
phases.  According  to  Briggs  and  Schmidt,9  the  two  essential  require- 


sRalston:   M.  &  S.  P.,  Vol.  CXI,  No.  17,  p.  623  (Oct.  23,  1915). 
»Briggs  and  Schmidt:  Jour.  Phys.  Chem.,  Vol.  XIX,  No.  6,  p.  470   (June 
1915). 


160  FLOTATION 

ments  of  an  emulsifying  agent  are  :  ( 1 )  The  property  of  condensing  by 
adsorption  in  the  dineric  interface;  and  (2)  the  ability  to  form  under 
these  circumstances  a  strong  coherent  film.  Temperature  is  a  decisive 
factor  in  emulsification,  for  its  effect  is  to  reduce  the  interfacial  ten- 
sion between  phases  and  also  to  lower  the  viscosity  of  the  phases.  In 
the  production  of  emulsions,  a  considerable  amount  of  surface  energy 
is  produced  because  of  the  relatively  large  surface  area  of  the  disperse 
phase  j  an  emulsion  is  the  more  speedily  effected  if  such  surface  energy 
be  reduced  by  the  use  of  a  liquid  having  a  low  surface-tension  as  the 
continuous  phase.  Some  emulsions,  under  certain  conditions,  display 
a  great  increase  in  viscosity  over  that  of  either  of  the  immiscible 
phases,  for  example,  the  emulsions  of  the  Pickering  order — up  to  99% 
of  oil  in  1%  of  soap  solution — can  be  cut  into  cubes.  Any  emulsion 
produced  with  soap  solution  is  at  once  destroyed  by  the  addition  of 
acid,  as  the  latter  will  decompose  the  soap. 

If  solid  particles  are  suspended  in  a  liquid,  they  tend  to  increase 
the  viscosity  of  that  liquid  gradually,  depending  on  the  amount  of  solid 
particles  present.  Experiments  have  shown  that  whenever  a  substance 
in  suspension  is  wetted  by  two  immiscible  liquids  simultaneously,  it 
will  go  into  the  dineric  interface  in  the  manner  already  mentioned,  and 
will  tend  therefore  to  produce  an  emulsion.  If,  however,  the  sus- 
pended particles  cannot  coalesce,  owing  to  adsorbed  oil  film  or  for  other 
reasons,  and  thus  effect  the  production  of  a  coherent  film,  the  emulsion 
will  not  be  stable.  Few  data  are  available  on  the  production  of  emul- 
sions by  the  oils  used  in  flotation  work,  or  on  the  matter  of  interfacial 
tensions  between  such  oils  and  water.  However,  we  are  no  doubt  deal- 
ing with  emulsified  or  partly  emulsified  pulp  in  some  of  the  flotation 
processes,  in  the  oil-froth  process  at  least. 

ELECTROLYTIC  AND  ELECTRO-STATIC  PHENOMENA.  Any  substance 
placed  in  contact  with  water  or  many  other  liquids  will  assume  an  elec- 
tric charge,  the  origin  of  which  is,  as  yet,  not  set  forth.  Most  sub- 
stances when  in  contact  with  water  become  negatively  charged,  but 
these  charges  can  be  differed  at  will  or  reversed  by  the  addition  of  the 
proper  electrolyte  in  requisite  amount.  These  electric  charges  are  by 
no  means  confined  to  sub-microscopic  particles,  but  are  found  also  on 
the  particles  of  a  coarse  suspension.  Gangue  minerals,  such  as  quartz, 
when  suspended  in  water,  are  negatively  charged,  and  sulphide  min- 
erals, such  as  pyrite,  are  positively  charged  under  like  conditions.  Oil 
drops  are  negatively  charged,  as  are  air  bubbles  under  certain  condi- 
tions. These  charges  are  very  minute  when  referred  to  the  mass  of  the 
particle..  Substantial  evidence  is  at  har^d  to  show  that  floatable  min- 


THE    FLOTATION    OF    MINERALS  161 

orals  have  the  positive  sign  of  electricity  when  suspended  in  water  or 
can  be  made  to  assume  that  sign  by  the  addition  of  proper  electrolytes 
in  sufficient  amount.  As  Callow10  observes,  there  is  a  parallelism  be- 
tween electro-static  characteristics  and  the  flotative  properties  of  ores. 
Many  of  the  electro-static  principles  have  either  been  carried  too  far 
or  misapplied,  as  recent  work  shows. 

Experiments  in  colloid  chemistry  indicate  that  the  contact  films  are 
charged  and  that  such  charges  affect  the  dispersion  or  coherence  of  the 
particles  in  suspension.  Of  course,  oppositely  charged  contact-films 
will  coalesce  while  similarly  charged  contact-films  will  repel  each  other, 
if  the  charges  are  sufficient  in  amount  to  overcome  the  force  of  cohe- 
siveness ;  in  the  latter,  dispersion  is  the  result.  The  oil  and  air  contact- 
films  having  negative  charges  would  tend  to  attract  the  sulphide  parti- 
cles, but  further  than  this  possibility  electro-statics  probably  plays 
little  part  in  flotation. 

It  is  admitted  that  only  minerals  that  are  good  conductors  are 
suitable  to  flotation.  As  the  electrical  theory  contends,  electrified  bub- 
bles must  be  supplied  to  float  the  conducting  minerals  that  are  at- 
tracted, leaving  behind  those  that  are  not.  The  bubbles  in  flotation 
are  simply  air  spaces  contained  by  a  mantle  of  oil  or  of  water,  and  there 
is,  therefore,  nothing  within  to  bear  the  charge.  In  case  it  could 
carry  a  charge,  which  \vould  only  be  possible  by  the  presence  of  con- 
tained ionized  gases  or  water-vapor,  the  charge  would  be  speedily  dis- 
sipated by  contact  with  the  interfacial  boundary.  Then  in  order  that 
a  bubble  may  carry  a  charge  it  must  be  protected  by  a  dielectric  film. 
Further,  electro-statics  plays  probably  little  part  in  holding  the  sul- 
phide particles  and  the  gas  bubbles  together,  as  neither  the  bubble  nor 
the  particle  can  have  a  charge  of  sufficient  magnitude  when  referred  to 
the  size.  The  electrical  theory  has  been  strongly  championed  by  at 
least  one  writer11  and  has  been  tolerated  by  some  others.  A  recent  ar- 
ticle12 indicates  that  the  principles  of  electro-statics  have  been  consider- 
ably misapplied.  It  is  my  belief  that  ./electro-statics  may  be  a  small  con- 
tributing factor  in  flotation  in  a  manner  not  as  yet  understood  be- 
cause of  a  lack  of  information  concerning  charges  at  the  interfacial 
boundary  between  immiscible  phases,  for  example,  where  the  colloidal 


10 J.  M.  Callow:   Bulletin  A.  I.  M.  E.,  No.  108,  p.  2334  (December  1915). 

"Bains:  'The  Electrical  Theory  of  Flotation,'  M.  &  S.  P.,  Vol.  CXI,  No.  22, 
p.  824  (Nov.  27,  1915)  and  Bains:  'The  Electrical  Theory  of  Flotation,'  II, 
ibid.,  Vol.  CXI,  No.  24,  p.  883  (Dec.  11,  1915). 

isFahrenwald:  'The  Electro-statics  of  Flotation,'  ibid.,  Vol.  CXI,  No.  11,  p. 
375  (March  11,  1916). 


162  FLOTATION 

state  is  introduced  in  oil-water  emulsions.     Apparently,  the  electric 
theory  is  not  important. 

FROTH  AND  BUBBLES.  The  idea  has  been  abandoned  by  most  people 
that  a  low  surface-tension  is  the  essential  requirement  for  froth  forma- 
tion. As  mentioned  by  Coghill  in  a  recent  writing,13  the  contamina- 
tion of  the  liquid  with  an  impurity  that  will  cause  a  variable  surface- 
tension  is  the  real  requirement.  A  bubble  of  air  is  spherical  in  shape 
and  this  shape  can  only  be  maintained  if  the  external  pressure  exceeds 
the  internal  pressure.  Since  a  bubble  does  not  expand  per  se,  large 
bubbles  can  only  be  accounted  for  by  heat,  coalescence,  or  electrifica- 
tion. Viscosity  is  an  important  factor  in  froth-persistence,  as  it  in- 
creases the  tenacity  of  the  liquid  film  and  thus  prevents  ready  rupture. 
The  rupture  or  bursting  of  bubbles  is  explained  thus : 

1.  Concussion  upon  a  surface  film  deficient  in  the  requisite  vis- 
cosity and  variable  surface-tension. 

2.  Relief  of  pressure — here  the  gas  of  the  bubble  in  expanding  ex- 
erts a  pressure  exceeding  that  of  the  liquid  film. 

3.  Adhesive  force  of  the  entrained  gas  for  the  atmospheric  air. 

4.  Evaporation  of  the  liquid  film. 

Flotation  bubbles  will  burst  for  any  one  or  a  combination  of  these 
reasons. 

Solutions  in  which  the  continuous  phase  is  a  solution  of  soap,  vari- 
ous products  from  the  saponification  of  albumens,  etc.,  will  froth  vol- 
uminously even  in  a  very  diluted  condition ;  frothing  never  occurs  in 
pure  liquids  and  is  a  definite  proof  that  the  solute  or  disperse  phase 
lowers  the  surface-tension  of  the  solvent.  A  froth,  which  shows  ad- 
sorption at  the  interfacial  boundary  of  solution  and  gas,  depends  for 
its  persistence  on  the  production  of  a  viscous  film  at  that  boundary ; 
these  viscous  films  are  the  direct  result  of  surface  adsorption  of  the  dis- 
perse phase,  that  is,  dissolved  contaminants,  the  amount  of  which  is 
small — disappearingly  so.  The  work  of  Hall  and  of  Miss  Benson  shows 
that  in  a  foaming  liquid  the  foam*is  richer  in  the  dissolved  contamin- 
ant than  is  the  bulk  of  the  liquid.  Froth  formation  in  the  Callow  cell 
is  the  result  of  the  injection  of  air  into  the  pulp  (already  emulsified)  ; 
the  froth  persists  as  long  as  there  is  sufficient  air  injected  into  pulp  of 
the  proper  consistence.  The  froth  in  the  Callow  cell  is  governed  in 
nature  by  the  kind  of  oil  used  and  by  the  amount  of  air.  A  pneumatic 
froth  is  unstable  or  ephemeral ;  it  dies  rapidly  when  removed  from  the 
influence  of  the  injected  air.  The  mechanical  froth,  on  the  other  hand, 


is'The  Science  of  a  Froth/  M.  &  S.  P.,  February  26,  1916. 


THE    FLOTATION    OF    MINERALS  163 

is  thick  and  persistent,  and  must  be  broken  up  in  dewatering  the  con- 
centrates. 

OILS  have  a  selective  action  for  metallic  sulphides,  tellurides,  and 
some  other  minerals.  The  fact  that  both  the  oil  and  the  air  or  other 
gas  have  a  selective  adhesion  for  sulphides  prevents  them  from  being 
wetted  by  water.  Conversely,  the  quartz  and  other  minerals  exhibit 
just  the  opposite  characteristics.  The  gangue-minerals,  generally,  do 
not  exhibit  adhesion  for  either  gas  or  oil ;  hence  they  are  readily  wetted 
by  water.  Gases  have  a  well-defined  adhesiveness  for  oils;  therefore 
the  air  or  gas  adheres  strongly  to  the  oil  film.  The  stability  of  a  froth 
depends,  in  the  main,  on  the  kind  of  oil  used,  for  example,  pine-oil 
makes  a  weak  brittle  froth,  and  creosote  makes  a  stable  elastic  froth. 
The  work  of  Devaux14  on  oil  films  explains  how  so  small  an  amount  of 
oil  as  is  used  in  the  various  flotation  processes  can  be  so  efficacious. 
From  a  consideration  of  the  immiscible  oil-water  interface,  if  any  oil 
will  film  the  internal  surface  of  a  gas  bubble  the  sulphide  particles 
would  be  contained  in  the  oil-water  interface  no  matter  what  the 
nature  of  the  gas  contained  by  the  water  film.  The  sulphide,  if  it 
enters  the  oil  phase,  would  then  present  an  oiled  surface  to  the  water 
phase.  There  are  three  conditions  then:  (1)  The  mineral  enters  the 
oil  phase  completely;  or  (2)  the  mineral  enters  the  water  phase  com- 
pletely; or  (3)  the  mineral  enters  the  oil-water  interface. 

Experiments  made  to  determine  the  nature  of  the  frothing,  select- 
ive, and  collective  action  of  different  oils  show  some  interesting  results. 
I  made  tests  on  a  zinciferous  slime  from  Joplin  with  different  oils,  the 
results  obtained  indicating  that  a  definite  mixture  of  oils  will  effect 
better  recoveries  than  any  one  oil  alone.  The  best  combination  con- 
sisted of  pine-oil  as  a  frother,  plus  wood-creosote  as  a  frother  and 
selector,  plus  refined  tar-oil  as  a  froth  stiffener. 

In  general,  pine-oil  makes  a  brittle  froth,  which  immediately  dies; 
creosotes  make  a  more  elastic  froth,  the  bubbles  of  which  may  expand 
to  3  in.  diam.  or  more  before  rupture.  Coal-tar  products  are  poor 
frothing  agents  and  if  used  must  be  aided  by  either  creosote  or  pine- 
oil  to  produce  a  good  froth.  Oils  of  a  lubricating  nature  seem  to  be 
of  little  value  in  flotation,  while  such  light  oils  as  gasoline  and  naphtha 
are  of  value  only  for  thinning  the  heavy  coal  and  wood  tars. 

AIR  AND  GAS.  At  this  time,  there  are  three  ways  by  which  a  gas 
may  be  forced  into  a  solution  mechanically,  as  follows : 


i*Devaux:   'Oil  Films  on  Water  and  on  Mercury,'  Smithsonian  Report  of 
1913,  p.  261. 


164  FLOTATION 

1.  By  beating  it  into  the  solution  by  means  of  paddles,  as  in  the 
Minerals  Separation  and  similarly  mechanically  agitated  machines. 

2.  By  pneumatic  means,  as  in  the  Callow  cell,  where  the  air  is  di- 
vided by  the  porous  blanket-bottom  into  minute  sprays. 

3.  By  so-called  liquid  jets,  as  in  a  process  recently  patented  in 
which  the  air  is  introduced  as  a  surface  film  surrounding  a  liquid  jet 
by  surface-tension. 

Conversely,  there  are  three  methods  by  which  dissolved  gas  may 
be  expelled  from  a  liquid : 

1.  When  the  liquid  is  super-saturated,  the  excess  gas  is  expelled. 

2.  By  heating  the  liquid,  when  some  of  the  gas  is  expelled  owing 
to  an  increase  in  its  volume. 

3.  By  pressure  reduction,  as  in  the  Elmore  vacuum  process,  where, 
according  to  the  law  of  Henry,15  "the  amount  of  gas  dissolved  by  a  liq- 
uid is  proportional  to  the  pressure  to  which  the  gas  is  subjected." 

An  air  or  gas  bubble  on  being  introduced  into  a  liquid  is  at  once 
surrounded  by  a  film  of  the  liquid.  Such  a  bubble  will  rise  to  the  sur- 
face (carrying  the  metallic  sulphides  by  reason  of  the  forces  already 
mentioned)  on  account  of  gravitation,  by  which  is  meant  that  the  ad- 
herence of  the  air  to  the  liquid  is  less  than  the  force  of  gravity. 

RESUME.  From  a  consideration  of  the  foregoing,  it  is  believed  that 
the  theory  based  on  the  different  interfacial  tensions  involved  is  the 
dominating  one  at  this  time.  Probably  flotation  is  due  to  a  combin- 
ation of  complex  phenomena.  The  theory  based  solely  on  occlusion 
goes  * '  by  the  board, "  as  it  has  been  shown  that  the  contributing  effect 
of  this  phenomenon  has  been  interpreted  laxly.16  The  phenomenon 
of  electro-statics  may  be  a  small  contributing  factor,  but  recent  work 
indicates  that  the  principles  have  been  misapplied.  An  explanation 
more  in  consonance  with  fact  can  be  given  in  terms  of  the  interfacial 
tensions  involved,  without  postulating  either  occlusion  or  electro- 
statics. 

The  main  and  essential  requirements  for  froth  flotation  are:  (1) 
the  production  of  a  persistent  froth;  (2)  the  attachment  of  the  bub- 
bles of  air  to  the  sulphides  or  other  material  to  be  floated;  and  (3) 
the  maintaining  of  a  selective  action  by  the  froth  bubbles  for  the  sul- 
phides or  other  material  to  be  floated. 


is  Jones:    Elements  of  Physical  Chemistry,  p.  177,  1907. 

isRalston:    'Why  Do  Minerals  Float?'  M.  &  S.  P.,  Vol.  CXI,  No.  17,  p.  623 
(Oct.  23,  1915). 


PRINCIPLES    UNDERLYING    FLOTATION  165 


PRINCIPLES  UNDERLYING  FLOTATION 

By  JOEL  H.  HILDEBRAND 
(From  the  Mining  and  Scientific  Press  of  July  29,  1916) 

INTRODUCTION.  *The  phenomena  involved  in  ore  flotation  are 
mostly  effects  of  surface-tension,  so  that  an  understanding  of  this 
force  and  how  it  may  be  modified  by  various  factors  is  fundamental  to 
a  scientific  study  of  flotation. 

Wherever  different  phases  are  in  contact  we  have  surfaces  where 
the  effects  of  surface-tension  may  be  apparent.  It  will  be  convenient, 
for  our  purposes,  to  classify  the  boundaries  between  phases  as  fol- 
lows: (1)  liquid-gas,  (2)  liquid-liquid,  (3)  liquid-solid.  The  bound- 
aries solid-gas  and  solid-solid  will  not  be  considered,  being  unim- 
portant from  the  standpoint  of  our  subject.  Since  the  effects  of  sur- 
face-tension are  increased  as  the  surface  between  the  phases  increases 
in  extent,  we  will  be  led  to  consider  the  systems  encountered  in  flota- 
tion processes,  in  which  one  of  the  phases  is  highly  dispersed.  These 
systems,  corresponding  to  the  above  classifications  are  (1)  foams,  in 
which  the  gas  is  highly  dispersed  in  the  liquid  (the  other  system, 
fog,  in  which  the  liquid  is  dispersed  in  the  gas  does  not  here  concern 
us);  (2)  emulsions;  (3)  suspensions. 

LIQUID-GAS  BOUNDARY,  (a)  Definition  and  Measurement  of  Sur- 
face-Tension. It  is  found  that  all  liquids  have  a  tendency  to  assume 
a  form  which  will  have  the  smallest  surface.  Where  the  liquid  is  sup- 
ported by  a  surface  that  it  does  not  wet  it  tends,  for  example,  to 
assume  a  spherical  form,  manifest  especially  with  small  drops,  where 
the  influence  of  gravity  is  small.  A  soap-bubble  tends  to  contract, 
expelling  the  air  through  the  orifice  of  the  pipe  from  which  it  is 
blown.  A  liquid  that  wets  the  walls  of  a  tube  will  be  drawn  up  into 
it.  The  magnitude  of  this  force  can  be  measured  by  various  methods, 
such  as  the  rise  in  a  capillary  tube,  the  shape  of  a  drop  under  the 
opposing  action  of  surface-tension  and  gravity,  the  weight  of  a  drop 
that  surface-tension  will  support  as  a  liquid  issues  slowly  from  a  tip 
of  definite  size.  A  general  idea  of  the  magnitude  of  this  force  may  be 
obtained  from  the  values  given  in  Table  I. 


*Abstract  of  an  illustrated  lecture  delivered  before  a  joint  meeting  of  the 
San  Francisco  section  of  the  American  Institute  of  Mining  Engineers  and 
the  California  section  of  the  American  Chemical  Society,  February  15,  1916. 


166  FLOTATION 

TABLE  I 

Temperature,        Surface-Tension, 

Liquid  °C.  Dynes  per  Cm. 

Hydrogen -252  2 

Carbon  di-sulphide  20  33.5 

Alcohol 20  22 

Water 20  73 

Ether    20  16.5 

Mercury  18  436 

Gold    1070  612 

Sodium  sulphate  880  187 

(b)  Cause  of  Surface-Tension.  It  must  be  noted  that  we  can 
define  and  measure  surface  tension  without  making  any  assumptions 
whatever  as  to  what  causes  it.  The  fact  that  the  surface  tends  to 
contract  with  a  definite  force  does  not  mean  that  the  surface  is  coated 
with  anything  like  a  rubber  memb ranee.  The  surface  of  a  liquid, 
except  for  a  slight  difference  in  density,  is  doubtless  the  same  as  the 
rest  of  the  liquid.  The  existence  of  surface-tension  is  to  be  attributed 
to  inter-molecular  attraction.  Consider  a  molecule,  such  as  a  in  Fig. 
1,  in  the  interior  of  a  liquid.  It  will  be  attracted  by  the  surrounding 


molecules,  and  these  attractions  may  be  resolved  axially  into  four  equal 
components,  as  shown  in  the  figure.  Consequently  nothing  but  viscous 
resistance  would  oppose  the  moving  of  this  molecule  to  another  por- 
tion of  the  liquid,  provided  it  remains  in  the  interior.  The  moment, 
however,  it  approaches  sufficiently  near  the  surface,  the  upward  com- 
ponent of  molecular  attraction  is  reduced,  becoming  zero  at  the  surface 
at  &,  if  we  neglect  any  effect  of  gas  or  vapor  above  the  surface.  The 
result  is  that  we  have  to  do  work  upon  each  molecule  brought  from 
the  interior  to  the  surface  of  a  liquid,  and  any  considerable  extension 
of  its  surface  involves  the  doing  of  a  considerable  amount  of  work 
against  a  force  the  component  of  which  along  the  surface  of  the  liquid 
we  call  'surface-tension.' 

(c)     Effect  of  Temperature.     Since  Jhe  increase  in  kinetic  energy 


PRINCIPLES    UNDERLYING    FLOTATION  167 

of  the  molecules  with  temperature  forces  them  farther  apart  we  should 
expect  inter-molecular  attraction  and  hence  surface-tension  to  dimin- 
ish with  increasing  temperature,  and  such  is  indeed  the  case.  At  the 
critical  temperature,  where  the  density  of  the  vapor  becomes  the  same 
as  that  of  the  liquid,  the  surface-tension  becomes  zero,  of  course. 

(d)  Effect  of  Dissolved  Substances.    The  surface-tension  of  mix- 
tures of  liquids  is  usually  less  than  that  which  would  be  calculated  on 
an  additive  basis,  so  that  the  more  general  tendency  is  for  solutes  to 
lower  the  surface-tension  of  the  solvent.     We  find  that  the  surface- 
tension  of  water  is  usually  raised  by  dissolved  salts,  and  lowered  by 
other  liquids,  and  especially  by  organic  colloids,  such  as  albumen,  glue, 
soap,  saponin,  etc.    Moreover,  it  is  possible  to  show  thermo- dynamic- 
ally that  solutes  which  lower  the  surface-tension  of  the  solvent  tend  to 
concentrate  at  the  surface,  still  further  lowering  the  surface-tension 
there.     For  this  reason  very  different  figures  are  obtained  for  static 
and  dynamic  measurements  of  surface-tension  with  solutions  of  such 
substances.     Table  II  shows  the  results  of  such  measurements  with 
sodium  oleate  (soap)  solutions. 

TABLE  II 

Surface-Tension, 

Concentration,  Dynes  per  Cm. 

%  Static        Dynamic 

0.025    55                   79 

0.25      26                   79 

1.25      26                   62 

2.5        26                   58 

It  will  be  seen  that  where  time  is  allowed  for  the  concentration  of 
the  soap  at  the  surface  the  tension  is  much  less  than  in  the  dynamic 
method,  where  no  time  is  allowed  for  the  effect  to  be  manifest.  This 
behavior  is  exceedingly  important  in  connection  with  the  stability  of 
foams,  emulsions,  etc.,  as  we  shall  see. 

(e)  Stability  of  Foams.     Since  the  production  of  a.  foam  (or  a 
mist)  from  a  liquid  involves  an  enormous  increase  in  surface,  and  con- 
sequent performance  of  work  against  surface-tension,  such  a  system 
is  unstable  unless  stabilized  by  some  means.    Drops  or  bubbles  tend  to 
coalesce,  hence  pure  liquids  never  foam.     To  produce  a  stable  foam 
requires  a  film  that  is  stable.     The  chief  condition  for  this  is  the 
presence  of  a  solute  that  will  be  strongly  adsorbed  at  the  surface  of 
the  solution,  lowering  its  surface-tension,  as  explained  above.     How 
this  will  give  a  stable  film  may  be  understood  by  the  aid  of  Fig.  2, 
which  represents  a  film  of  solution,  the  shading  indicating  the  greater 
concentration  at  the  surface.    If  such  a  film  should  be  stretched,  be- 
coming thinner  at  some  portion,  as  at  a,  the  new  surface  formed  by 


168 


FLOTATION 


FIG.  2 


the  stretching  would  contain  less  solute,  the  time  not  being 
sufficient  for  adsorption,  and  hence  would  be  stronger  than 
the  old  surface.  It  is  obvious  that  such  a  film  would  be 
stable,  automatically  becoming  stronger  wherever  rupture 
is  threatened.  This  is  the  action  of  the  foaming  agent,  such 
as  pine-oil,  used  in  flotation  processes.  Here,  of  course,  a 
foam  of  great  stability  is  undesirable,  as  it  must  be  broken 
down  later. 

Other  factors  of  minor  importance  in  foam  stability  are 
viscosity,  which  retards  the  draining  of  the  film  (hence  the 
frequent  addition  of  glycerine  to  soap-bubbles)  ;  small 
volatility,  preventing  evaporation  of  the  foam  where  ex- 
posed to  the  air;  and  the  protection  of  the  bubbles  from 
coalescence  by  the  forming  of  a  skin  or  armor  about  them. 
The  particles  of  solid  ore  present  in  the  foam  in  flotation 
processes  undoubtedly  act  in  this  way. 

LIQUID-LIQUID  BOUNDARY.  Much  that  has  been  said  ap- 
plies here.  Methods  of  measurement  are  similar.  The 
magnitudes  of  these  interfacial  tensions  are  illustrated  in 

Table  III. 

TABLE  III 


Boundary 

Mercury-water   

Benzene-water    

Turpentine-water 

Methyl  alcohol-carbon  di-sulphide. 


Surface-Tension, 
Dynes  per  Cm. 
370 
33 

12 

0.82 


This  surface-tension  becomes  zero  at  the  critical  temperature  of 
mixing  of  the  liquids,  and  it  is  affected  by  dissolved  substances  accord- 
ing to  the  same  principles  as  apply  to  the  simpler  systems. 

(a)      The  Spreading  of  Drops.     The  spreading  of  drops  of  oil 


upon  water  to  form  an  exceedingly  thin  film  is  familiar  to  all. 
Whether  or  not  this  phenomenon  takes  place  depends  .upon  the  mag- 
nitudes of  the  three  surface-tensions  indicated  in  Fig.  3,  which  repre- 
sents a  drop  of  a  lighter  liquid  placed  upon  a  heavier  one  with  which 


PRINCIPLES    UNDERLYING    FLOTATION  169 

it  does  not  mix.  Obviously  the  drop  will  spread  out  over  the  surface 
whenever  the  surface-tension  represented  by  a  is  greater  than  the  sum 
of  b  and  c.  When  a  <  b  +  c  the  drop  will  remain  in  lens  form 
upon  the  other  liquid.  One  of  these  cases  may  be  converted  into 
the  other  by  the  addition  of  suitable  solutes  to  one  phase.  For  ex- 
ample, although  oil  usually  spreads  upon  water,  where  the  surface- 
tension  of  the  water  is  much  lowered,  as  it  is  in  meat-broth  by  the 
presence  of  albumin,  gelatin,  etc.,  the  value  of  a  is  small  enough  to 
allow  any  oil  present  to  remain  as  lens-shaped  drops. 

(b)  The  Stability  of  Emulsions.  This  is  obviously  favored  by  a 
low  surface-tension  between  the  phases,  by  viscosity,  by  the  presence 
of  a  substance  tending  to  form  a  skin  preventing  the  droplets  of  the 
enclosed  phase  from  coalescing,  as  they  naturally  tend  to  do,  and 
most  important  of  all,  the  presence  in  the  -phase  that  is  to  enclose  the 
other  of  a  substance  that  will  be  positively  adsorbed  at  its  surface, 
thus  making  stable  a  film  of  the  liquid  separating  two  droplets  of  the 
other,  enclosed,  liquid.  The  enclosed  phase  takes  the  place  of  the 
bubbles  in  the  previous  discussion  of  foam  stability.  By  a  suitable 
choice  of  solutes  either  phase  may  be  made  the  enclosed  phase.  For 
example,  when  soap  is  added  to  water  the  films  of  water  become  stable, 
and  a  liquid  like  benzene  may  be  made  to  form  a  stable  emulsion  in 
water.  On  the  other  hand,  when  a  magnesium  soap  is  dissolved  in 
benzene,  films  of  benzene  become  stable,  and  benzene  will  yield  both 
stable  foams  and  stable  emulsions  with  water  as  an  enclosed  phase. 

LIQUID-SOLID  BOUNDARY.  With  a  boundary  of  this  sort  direct 
measurement  of  surface-tension  is  impossible,  but  relative  values  may 
be  inferred  by  noting  the  wetting  power  of  a  liquid  for  a  solid, 
especially  as  indicated  by  the  angle  of  contact.  When,  for  example, 
a  drop  of  water  is  placed  upon  a  bright  metal  surface,  instead  of 
spreading  over  the  surface  of  the  latter  as  would  kerosene,  it  remains 
in  drop  form,  its  surface  meeting  the  metallic  surface  at  a  certain 
angle.  When  a  drop  of  castor-oil  is  placed  on  the  metal  it  forms  a 
much  flatter  drop,  the  angle  being  different,  corresponding  to  greater 
wetting  power  for  the  metal.  The  surface-tension  between  these 
phases  can  be  altered  as  before  by  the  addition  of  adsorbed  solutes, 
so  that  a  drop  of  soap  solution  will  be  much  flatter  when  placed  upon 
the  metal  than  the  drop  of  pure  water.  This  wetting  power  is  also 
different  for  the  same  liquid  upon  different  solids,  as  is  illustrated 
by  the  experiment  shown  in  Fig.  4,  where  the  angles  of  contact  indicate 
that  when  chloroform  and  water  are  in  competition  the  former  has 
greater  wetting  power  for  a  metal  surface,  while  the  latter  has  greater 


170 


FLOTATION 


<0 


wetting  power  for  glass.     It  would  seem  that  determinations  of  these 
angles  should  offer  a  valuable  preliminary  to  flotation  experiments. 

As  a  consequence  of  this  relative  wetting  power,  if  a  layer  of  kero- 
sene is  placed  over  water,  and  a  powdered  silicious  material  dropped 
into  the  vessel,  it  will  stop  only  momentarily  at  the 
oil-water  surface.  As  fast  as  the  oil  can  be  displaced 
by  the  water  the  particles  drop  through  into  the  water 
phase.  If,  however,  a  metallic  powder,  or  a  sulphide 
with  metallic  lustre,  be  dropped  into  the  vessel,  it  re- 
mains in  the  oil  phase,  supported,  if  the  mass  is  not 
too  great,  by  the  surface-tension  at  the  boundary. 

The  ease  with  which  a  solid  particle  can  float  on 
the  surface  of  a  lighter  liquid  depends  upon  its  size, 
Q)        ^  the  difference  in  density  of  solid  and  liquid,  and  the 

angle  of  contact  the  liquid  makes  with  the  solid.  The 
relationship  is  expressed  in  Fig.  5,  where  we  assume, 
for  simplicity,  a  cylindrical  particle  of  radius  r, 
height  h,  and  density  d,  floating  on  a  liquid  of  density 
d.2  and  surface-tension  s.  The  maximum  effect  that 
could  be  exerted  by  gravity  upon  the  particle  would 
obviously  be  irr~hg  (dl-d2)  dynes.  If  the  solid  were 
not  wet  at  all  by  the  liquid  and  the  angle  of  contact 
were  zero,  the  upward  force  tending  to  prevent  the 
particle  from  sinking  into  the  liquid  would  be  2-n-rs. 
In  an  actual  case,  however,  where  this  angle  is  a,  the 
upward  force  is  2-jrrs  cos  a.  It  is  obvious  that  the  float- 
ing tendency  would  be  greater  the  smaller  the  particle,  the  less  its 
density  relative  to  that  of  the  liquid,  the  greater  the  surface-tension  of 
the  liquid,  and  the  smaller  a.  In  floating  practice  the  densities  are 
not  to  be  altered,  the  size  of  the  particles  is  made  as  small  as  is  con- 
sistent with  economical  grinding  and  subsequent  recovery,  the  surface- 
tension  of  the  water  cannot  be  increased,  but  is  rather  decreased  by 
the  agent  added  to  produce  foaming.  The  foaming  gives  a  large  sur- 
face, as  the  total  quantity  of  ore  floated  is  proportional  to  the  surface 
of  the  water  and  not  to  its  volume.  The  most  effective  modification 
that  can  be  made  in  the  above  factors  is  to  decrease  the  angle  a  as 
much  as  possible  for  the  ore  particles,  while  still  leaving  it  greater 
than  90°  for  the  gangue  particles,  the  condition  necessary  that  the 
latter  should  sink.  This  is  the  purpose  of  the  small  quantity  of  oil 
added  during  the  grinding  of  the  ore.  The  wetting  power  of  oil  for  a 
metallic  surface  causes  the  oil,  if  the  right  kind,  to  spread  over  the 


<5 


a 


FIG.  4 


PRINCIPLES    UNDERLYING    FLOTATION 


171 


metallic  surface  as  it  would  over  the  surface  of  water.  The  water 
present  at  the  same  time  wets  the  gangue  preferentially,  preparing 
for  the  separation  that  results  when  the  large  amount  of  water  is 
added.  It  is  obvious  that  the  frothing  agent  necessarily  added  later 
works  against  the  effect  here  desired  of  the  least  possible  wetting  of 
the  ore,  as  it  decreases  the  surface-tension  both  at  the  liquid-air  and 
at  the  liquid-solid  surfaces. 

A  word  might  be  said  in  conclusion  about  the  stability  of  suspen- 
sions. Besides  the  stabilizing  influences  important  in  the  case  of 
foams  and  emulsions,  another  here  rises  to  great  importance,  namely, 
the  electric  charges  on  the  suspended  particles  due  to  adsorbed  ions. 


\>  \\li\\\\\ 

x\  \   ,f  !\  \\x    0 


FIG.  5 


This  effect  may  be  illustrated  by  dividing  a  suspension  of  fine  silica 
into  two  portions,  and  adding  to  one  a  little  acid  and  to  the  other  a 
little  alkali.  It  is  found  that  in  the  second  case  the  suspension  is 
quickly  flocculated  and  settles  out,  while  in  the  acid  solution  it  re- 
mains suspended  for  a  long  time.  Reference  must  be  made  to  works 
upon  colloids  for  further  discussion  of  the  many  interesting  phe- 
nomena connected  with  such  behaviors.  In  ore  flotation,  the  effect  of 
even  slight  amounts  of  acid  or  alkali  may  be,  aside  from  that  just 
mentioned,  to  clean  the  ore  particles  and  thus  expose  a  more  truly 
metallic  surface  to  the  oil,  and  to  affect  the  surface-tensions  in- 
volved, especially  by  modifying  chemically  the  other  substances  added, 
notably  the  frothing  agent. 


172  FLOTATION 


MOLECULAR  FORCES  AND  FLOTATION 

BY  WILL  H.  COGHILL 
(From  the  Mining  and  Scientific  Press  of  September  2,  1916) 

The  warning  about  young  men  specializing  in  flotation,  as  sounded 
by  E.  P.  Mathewson  in  a  recent  number  of  the  Mining  and  Scientific 
Press,  should  be  considered  by  all  who  are  directing  these  men  in  their 
education.  It  provokes  the  question  that  ever  confronts  the  instructor 
in  a  technical  school. 

The  student  may  be  drilled  on  the  design  and  construction  of  the 
various  flotation  machines,  and  the  methods  and  results  of  the  experi- 
menters, and  be  sent  into  the  field  feeling  that  he  is  strictly  up-to-date, 
but  his  school- work  would  not  amount  to  much  if  he  has  been  taught 
only  the  ever-changing  art.  He  would  have  acquired  something  more 
enduring  and  be  better  prepared  to  benefit  from  his  college  course  had 
he  been  taught  natural  laws  with  enough  of  the  art  to  give  a  view  of  the 
field  to  which  the  laws  could  be  applied,  for  man's  methods  are  ever 
changing  while  Nature's  laws  are  invariable.  The  processes  of  a  few 
years  ago  are  now  obsolete,  but  the  principles  upon  which  they  were 
founded  will  be  applied  to  new  methods  for  generations  to  come. 

To  the  workers  in  flotation  has  fallen  the  problem  of  outlining  the 
rudiments,  and  then  by  means  of  laboratory  experiment,  made  by  aid 
of  the  results  of  workers  in  the  related  sciences,  developing  flotation  to 
the  point  where  scientific  reasoning  may  be  applied  to  direct  tests  on 
ores  as  is  now  done  in  cyanidation.  It  took  twenty  years  to  develop 
the  science  of  the  cyanide  process.  It  will  take  as  long  in  flotation  if 
we  continue  our  antiquated  methods.  So  far  as  I  can  learn,  not  more 
than  two  of  the  great  number  of  recent  contributors  of  articles  on  flota- 
tion have  had  an  opportunity  for  a  deliberate  study  of  the  related  sci- 
ences. The  rest  of  us  have  a  job  to  look  after  and  are  busy  enough  at- 
tending to  it.  Advancement  is,  therefore,  slow.  The  papers  by  0.  C. 
Ralston  and  E.  E.  Free  are,  of  course,  excellent.  But  in  many  cases 
they  shoot  above  our  heads ;  for  this  we  and  not  they  are  to  blame. 

The  majority  of  the  workers  in  flotation  who  have  had  the  advant- 
age of  a  school  of  mines  training  have  taken  only  the  prescribed  four 
years  and  then  hurried  into  the  business  of  mining.  Their  love  for  sci- 
ence was  none  too  great  when  they  left  school  and  the  constant  employ- 
ment in  the  art  has  in  no  way  tended  to  increase  it.  By  a  careful  read- 


MOLECULAR    FORCES  173 

ing  of  the  articles  mentioned  they  might  hope  to  glean  some  fact,  the 
knowledge  of  which  would  be  of  aid  in  the  art  of  metallurgy,  but  the 
material  is  entirely  too  heavy  for  one  who  has  not  had  a  special  train- 
ing in  science. 

We  should  learn  to  think — not  parrot  the  statements  of  others — in 
terms  of  the  molecules  before  science  will  be  of  aid  to  us  in  flotation. 
We  cannot  adjust  ourselves  to  this  in  a  moment.  It  requires  time  and 
effort.  Many  of  us  have  sat  aghast  while  an  astronomer  spoke  of  dis- 
tances in  terms  of  the  diameter  of  the  earth.  We  must  now  go  to  the 
other  extreme  and  become  familiar  with  molecular  dimensions.  This 
requires  much  study,  but  in  it  we  acquaint  ourselves  with  the  observa- 
tions of  physicists  and  chemists  so  that  we  are  not  likely  to  spend  val- 
uable time  in  discovering  something  that  is  already  known. 

The  mastery  of  science  is  not  easy.  While  in  school  we  had  to 
learn  the  chapters  page  by  page,  but  this  does  not  seem  to  be  the  best 
way  for  those  without  an  instructor.  To  advise  one  to  go  through  a 
book  rapidily,  gathering  only  an  idea  here  and  there,  and  through  it 
again,  may  seem  to  be  superficial.  But  the  aim  is  to  master  the  subject 
and  this  is  doubtless  the  way  to  do  it.  This  method  of  study  is  en- 
dorsed by  Dr.  V.  H.  Gottschalk1  when  he  says:  "After  several  read- 
ings of  the  short  paper  on  .  .  .  ,  read  first  the  excellent  summaries 
at  the  end  of  ...  before  undertaking  a  rapid  survey  of  the  whole 
set ;  follow  this  by  a  more  careful  consideration  of  the  summaries  with 
re-reading  of  portions  of  the  text  when  necessary ;  continue  this  proc- 
ess until  the  drift  of  the  argument  begins  to  reveal  itself. ' ' 

f  One  contributor  has  said  that  the  scientific  man  has  aided  little  in 
flotation.  Indeed  he  is  correct,  and  so  is  the  old-timer  who  says  that 
more  mines  have  been  discovered  by  simple  prospectors  than  by  mining 
engineers.  The  ratio  of  those  who  pursue  the  right  methods  to  those 
who  have  no  method  at  all  is  as  1 : 1000. 

Have  any  of  the  big  companies  put  their  engineers  on  retainers  so 
that  they  could  review  the  fundamentals  of  science  and  pursue  post- 
graduate work  in  a  university  where  they  could  have  access  to  a  com- 
plete library?  Probably  none,  because  the  American  business  man 
goes  straight  for  the  dollar  and  must  see  the  wheels  turning  before  he 
is  assured  of  dividends. 

Some  of  the  blunders  that  have  crept  into  the  articles  on  flotation 
are  a  great  drawback  to  those  who  wish  to  learn  but  find  their  library 
incomplete.  One  writer  has  said,  for  example,  "the  cohesion  of  water 
varies  as  the  temperature  .  .  .  and  at  the  boiling-point  there  is  no 


iBibliography,  'Concentrating  Ores  by  Flotation,'  University  of  Missouri. 


174  FLOTATION 

cohesion."  This  statement  is  misleading.  Scientists  had  this  problem 
pretty  well  in  hand  nearly  a  century  ago  and  knew  that  surface-ten- 
sion became  zero  at  the  critical  temperature  and  not  at  the  boiling- 
point,  as  we  ordinarily  use  this  term.  Brunner2  recognized  this  fact  in 
1847  and  knew  that  surface-tension  decreases  with  rising  temperature 
until  the  critical  point  is  reached,  when  liquid  and  vapor  become  iden- 
tical and  surface-tension  is  zero. 

In  the  Smithsonian  Physical  Tables,  the  surface-tension  of  water  at 
100°  C.  is  given  as  61.5,  and  nothing  is  said  about  boiling-point. 

Since  critical  temperature  is  so  closely  related  to  surface-tension 
it  is  obvious  that  we  should  acquire  a  working  knowledge  of  it.  At  one 
time  it  was  considered  sufficient  for  us  to  be  able  to  say  that  critical 
temperature  was  the  temperature  above  which  a  gas  could  not  be  lique- 
fied no  matter  how  great  the  pressure.  This  served  the  purpose  for 
which  it  was  intended,  but  it  is  inadequate  for  us  now.  If  we  define 
it  as  the  temperature  at  which  the  surface-tension  between  a  liquid  and 
its  vapor  becomes  equal  to  zero,  and  any  meniscus  or  bounding  surface 
disappears,  we  have  added  to  our  knowledge  of  molecular  forces. 

It  follows  that  when  liquids  are  near  their  critical  point,  for  ex- 
ample, condensed  gases,  they  will  have  small  surface-tension,  while 
liquids  far  removed  from  their  critical  point,  such  as  molten  metals 
and  fused  salts,  will  have  large  surface-tensions. 

Liquid  carbon  dioxide  is  an  example  of  a  liquid  that  is  near  its  crit- 
ical point  at  atmospheric  temperature;  the  critical  temperature  is  31° 
C.  Its  surface-tension  is  therefore  very  small  unless  artificial  refrig- 
eration is  used. 

Mercury,  on  the  other  hand,  at  atmospheric  temperature,  is  so  far 
below  its  critical  point  that  it  would  be  expected  to  have  a  great  sur- 
face-tension, as  indeed  it  has. 

To  aid  further  in  getting  the  relation  of  critical  temperature  to 
surface-tension,  I  quote  from  Ferguson.3  He  indicates  their  relation 
and  the  basis  on  which  surface-tension  of  liquids  should  be  compared, 
saying:  "In  earlier  researches  on  the  subject,  comparisons  [surface- 
tension]  were  made  at  the  same  temperature,  but  it  was  recognized  by 
Schiff  that  surface-tension  should  be  compared  at  corresponding  tem- 
peratures, that  is,  at  temperatures  which  are  equal  fractions  of  critical 
temperatures  of  the  liquids  under  consideration. "  Continuing,  we 
find  him  stating  the  relation  of  critical  temperature  to  boiling-point, 
thus:  "Unfortunately  the  critical  temperature  of  comparatively  few 


2'Physical  Chemistry.'    Ramsey  and  Smiles. 
^Science  Progress,  January  1915.  • 


MOLECULAR   FORCES  175 

organic  compounds  have  been  directly  determined,  and  it  was  sup- 
posed that  these  conditions  were  fulfilled  at  the  boiling-point  of  the 
liquids  examined.  If  this  be  the  case  the  ratio  of  the  boiling-point  to 
the  critical  temperature  of  all  liquids  should  be  the  same  where  temper- 
atures are  measured  on  absolute  scale." 

The  degree  of  exactness  with  which  this  condition  is  fulfilled  is  re- 
markable, as  can  be  seen  by  an  examination  of  tables  published  by  Fer- 
guson, also  those  in  the  *  Handbook  of  Chemistry  and  Physics/  and 
elsewhere.  They  show  the  value  of  this  ratio  calculated  from  a  num- 
ber of  substances  of  very  diverse  boiling-points 

An  examination  of  these  tables  shows  that  it  is  a  fairly  accurate 
generalization  to  put 

Boiling  point  =  0.656  X  crit.  temp. 

where  temperatures  are  measured  on  the  absolute  scale ;  so  that  from 
the  boiling-point  we  can  calculate  the  critical  temperature  (subject  to 
an  error  of  not  more  than  5%  in  the  case  of  the  carbon  compounds). 
For  a  proof  that  vapors  as  well  as  liquids  are  regarded  as  having  mol- 
ecular cohesion,  one  has  only  to  refere  to  Van  der  Waal's  modification 
of  Boyle's  law. 

The  toy-balloon  theory4  that  each  molecule  of  water  is  drawn  to- 
ward the  centre  of  gravity  of  its  mass  cannot  be  taken  as  a  substitute 
for  the  accepted  theory  of  surface-tension,  for  it  is  not  in  accord  with 
physicists  either  here  or  abroad.  They  generally  agree  that  the  radius 
of  molecular  attraction  is  insensible  but  finite.  They  are  of  one  ac- 
cord in  the  opinion  that  "every  molecule5  attracts  every  other  molecule 
that  may  happen  to  be  within  a  certain  distance  from  it,  which  we  de- 
note as  the  sphere  of  molecular  attraction.  In  the  body  of  the  liquid, 
this  attractive  force  is  more  or  less  neutralized  by  the  fact  that  the 
molecule  we  are  considering  is  surrounded  on  all  sides  by  others,  all 
pulling  in  different  directions.  Hence  the  combined  effort  is  practic- 
ally zero.  At  the  surface,  however,  all  the  molecules  are  below  it,  and 
there  are  none  above  to  neutralize  the  force  they  exert.  There  is  thus  a 
strong  downward  force  tending  to  drag  the  molecule  into  the  surface. 
This  force  makes  itself  manifest  in  the  phenomenon  known  as  'surface- 
tension  '  or  '  capillarity. ' 

Methods  of  ore  dressing  today  fall  under  one  of  two  heads,  gravi- 
tation or  flotation.  The  fundamental  law  of  the  former  was  discovered 
by  Archimedes,  that  of  the  latter  by  Leslie.  Archimedes,  as  we  know, 


4Dudley  H.  Norris,  in  M.  &  S.  P.,  Feb.  12,  1916. 
•r>'Molecular  Physics.'    Crowther. 


176  FLOTATION 

while  in  his  bath,  noticed  the  loss  of  weight  of  his  own  body  and  it  oc- 
curred to  him  that  any  body  immersed  in  a  liquid  must  lose  a  weight 
equal  to  the  weight  of  the  liquid  displaced.  Leslie,  a  British  scientist, 
was  the  first  (1802)  to  give  a  correct  explanation  of  the  rise  of  a  liquid 
in  a  tube.6  Archimedes  considered  only  the  force  of  gravity  on  known 
masses;  Leslie  took  into  account  the  molecular  force.  It  is  Archimedes 
v.  Leslie.  Metallurgists  have  written  much  on  Archimedes'  law  and 
very  little  on  Leslie's,  the  latter  having  been  left  to  the  physicist  and 
chemist. 

It  is  surprising  how  little  attention  metallurgists  have  given  to  the 
application  of  the  physical  principle  discovered  by  Leslie.  Until  re- 
cently they  have  been  quite  satisfied  to  call  it  'capillarity'  and  let  it 
pass.  Capillarity  has  made  itself  manifest  to  us  in  many  ways.  Rich- 
ards speaks  of  it  in  his  'Textbook  of  Ore  Dressing'  under  the  subject  of 
amalgamation.  He  says  that  the  capillarity  of  mercury  is  negative  ex- 
cept with  those  metals  with  which  it  easily  amalgamates;  and  the 
trouble  due  to  grease  is  familiar  to  mill-men.  In  cupellation,  the  lead 
oxide  is  drawn  into  the  pores  of  the  cupel,  while  the  lead  ignores  them 
and  tends  to  shape  itself  into  a  sphere.  Were  it  not  for  molecular  co- 
hesion the  resulting  silver  bead  would  flatten  and  become  so  contami- 
nated by  the  cupel  that  its  subsequent  treatment  would  be  difficult. 
Galena7  penetrates  the  fire-brick  of  the  furnaces  in  which  it  is  treated. 
Often  a  network  of  small  veins  of  bright  crystalline  galena  is  found  in 
furnace-linings.  The  molecular  deportment  of  galena  and  litharge  is 
quite  different  from  that  of  lead  itself. 

In  zinc  smelting  it  is  necessary  to  re-work  the  'blue  powder'  be- 
cause the  film  of  oxide,8  which  coats  each  particle  of  zinc,  prevents  coa- 
lescence. The  forces  that  control  the  films  on  blister-steel  and  blister- 
copper  are  identical  with  those  that  maintain  the  form  of  the  soap- 
bubble. 

The  geologist  has  studied  the  bubbles  in  lava  and  has  found  that 
the  vesicles9  are  roughly  spherical.  This  spherical  shape  cannot  be 
maintained  unless  the  pressure  on  the  inside  is  greater  than  that  with- 
out. Only  surface-tension  can  account  for  this  excess.  He  is  also 
aware  that  if  the  wick  of  a  lamp  touches  water,10  the  latter  rises 


eSome  authorities  state  that  Laplace  first  developed,  about  1807,  a  theory 
of  capillary  action. 

7'Metallurgy  of  Lead.'    Hofman.    P.  8. 

^'Metallurgy  of  Zinc  and  Cadmium.'    Ingalls.    P.  526. 

s'Igneous  Rock  and  Their  Origin.'    Daly. 

lo'Role  and  Pate  of  Connate  Water  in  Oil  and  Gas  Sands,'  R.  H.  Johnson, 
Bull.  No.  98,  A.  I.  M.  E.,  p.  221;  also  'Capillary  Concentration  of  Gas  and  Oil,' 
C.  W.  Washburn,  Bull.  No.  93,  A.  I.  M.  E.  > 


MOLECULAR    FORCES  177 

through  the  capillaries  previously  filled  with  oil,  makes  the  flame  sput- 
ter, and  often  extinguishes  the  light.  In  the  same  way  water  will  pass 
from  the  coarse  spaces  of  the  sand  or  from  fissures  into  the  fine  capil- 
laries of  shale,  displacing  the  oil,  which  is  thereby  forced  into  the  sand 
through  neighboring  pores.  The  cohesion  that  holds  together  the  par- 
ticles of  a  crayon  and  adhesion  of  the  chalk  to  the  blackboard,  or  of 
dust  to  a  mirror,  are  all  evidence  of  molecular  force.  Many  of  the  ex- 
amples cited  come  under  'capillarity,'  but  since  that  is  difficult  to  de- 
fine and  is  therefore  likely  to  be  used  to  cloak  ignorance,  I  shall  not  at- 
tempt a  definition.  Molecular  cohesion  and  adhesion,  and  probably 
molecular  repulsion,  must  be  studied  in  detail. 

A  study  of  capillarity  is  of  great  aid  in  gaining  a  conception  of  the 
conduct  of  the  molecular  forces  of  cohesion  and  adhesion  that  cause 
some  substances  to  float  on  the  surface  of  a  liquid  while  others  sink.  I 
quote  from  a  high-school  book  on  physics,11  which,  to  my  mind,  gives 
one  of  the  first  lessons  in  the  science  of  flotation.  The  discussion  is  as 
follows :  "We  must  keep  in  mind  two  familiar  facts:  first,  that  the  sur- 
face of  a  body  of  water  at  rest,  for  example  a  pond,  is  at  right  angles 
to  the  resultant  force,  that  is,  gravity,  which  acts  upon  it ;  second,  that 
the  force  of  gravity  acting  upon  a  minute  amount  of  liquid  is  negligible 
in  comparison  with  its  own  cohesive  force.  Consider  then  a  very  small 
body  of  liquid  close  to  the  point  O  (Fig.  1)  where  water  is  in  contact 
with  the  wall  of  the  glass  tube.  Let  the  quantity  of  liquid  considered 
be  so  minute  that  the  force  of  gravity  acting  upon  it  may  be  disre- 
garded. The  force  of  adhesion  of  the  wall  will  pull  the  liquid  particles 
at  0  in  the  direction  of  OE.  The  force  of  cohesion  of  the  liquid  will 
pull  these  same  particles  in  the  direction  of  OF.  The  resultant  of  these 
two  pulls  on  the  liquid  at  0  will  then  be  represented  by  OR  (Fig.  1). 
If  then  the  adhesive  force  OE  exceeds  the  cohesive  force  OF,  the  direc- 
tion of  OR  of  the  resultant  force  will  lie  to  the  left  of  the  vertical  OM 
(Fig.  2)  in  which  case,  since  the  surface  of  the  liquid  always  assumes 
a  position  at  right  angles  to  the  resultant  force,  it  must  rise  up  against 
the  wall  as  water  does  against  glass.  If  the  cohesive  force  OF  (Fig.  3) 
is  strong  in  comparison  with  the  adhesive  force  OE,  the  resultant  OR 
will  fall  to  the  right  of  the  vertical,  in  which  case  the  liquid  must  be 
depressed  about  O.  Whether  then,  a  liquid  will  rise  against  a  solid 
wall  or  be  depressed  by  it  will  depend  only  on  the  relative  strength 
of  the  adhesion  of  the  wall  for  the  liquid  and  the  cohesion  of  the  liq- 
uid for  itself.  Since  mercury  does  not  wet  glass12  we  know  that  cohe- 


n'A  First  Course  in  Physics.'    Millikan  and  Gale. 

12It  is  a  well  known  fact  that  there  is  a  slight  adhesive  force  between 


178 


FLOTATION 


sion  is  here  relatively  strong,  and  we  should  expect,  therefore,  that  the 
mercury  would  be  depressed,  as  indeed,  we  find  it  to  be.  The  fact  that 
water  will  wet  glass  indicates  that  in  this  case  adhesion  is  relatively 
strong,  and  hence  we  should  expect  water  to  rise  against  the  walls  of 
the  containing  vessel,  as  in  fact  it  does.  As  soon  as  the  curvatures  just 
mentioned  are  produced,  the  concave  surface  aob  (Fig.  4)  tends,  by 
virtue  of  surface-tension,  to  straighten  out  into  a  flat  surface  ao^b. 
But  it  no  sooner  begins  to  straighten  out  than  adhesion  again  elevates 


FIG.  1 


FIG.  2 


FIG.  3 


FIG.  4 


FIG.  5 


FIG.  6 


it  at  the  edges.  It  will  be  seen,  therefore,  that  the  liquid  must  continue 
to  rise  in  the  tube  until  the  weight  of  the  volume  lifted  balances  the 
tendency  of  the  surface  to  flatten  out.  Similarly  a  convex  surface  aob 
( Fig.  5 )  falls  until  the  upward  pressure  at  o  balances  the  tendency  of 
the  surface  aob  to  flatten  out. ' ' 

If,  in  the  case  of  water  against  glass,  the  water  is  pulled  upward 
and  in  the  case  of  mercury  against  glass  the  mercury  is  pulled  down- 
ward, the  converse  must  also  be  true,  namely,  that  in  the  former  the 
glass  is  pulled  down  and  in  the  latter  the  glass  is  pushed  up. 

Now  assume  that  you  had  two  minerals  so  that  they  are  partly  sub- 
merged by  a  liquid  and  that  with  one  adhesion  is  very  great  (rela- 
tively) and  that  with  the  other  the  adhesion  is  very  slight.  It  is  obvious 


mercury  and  glass  and  that  mercury  exerts  an  attractive  force  upon  air,  but 
the  quotation  suffices  for  the  present. 


MOLECULAR    FORCES  179 

that  the  surface  of  the  liquid  will  turn  up  at  the  contact  with  the 
former  and  down  and  around  the  other,  and  that  if  these  particles  are 
so  small  that  the  force  of  gravity  is  negligible  it  is  impossible  for  the 
former  to  float  and  just  as  impossible  for  the  latter  to  sink.  One  of 
them  cannot  ride  on  the  surface  and  is  actually  drawn  into  the  liquid 
like  gold  into  mercury,  while  the  other  cannot  by  any  means  enter  the 
liquid  unless  its  mass  is  sufficient  to  overcome  the  contractile  force  in 
the  surface  of  the  depressed  liquid. 

This  process  of  reasoning  is  what  I  consider  to  be  a  natural  and  cor- 
rect result  of  the  study  of  the  cause  of  capillary  rise  and  depression  as 
presented  by  Millikan  and  Gale,  and  to  show  that  my  conclusions  are  in 
harmony  with  their  ideas  1  quote  them  again,  where  they  discuss  the 
floating  of  a  needle.  They  say :  "  So  long  as  the  needle  is  so  small  that 
its  own  weight  is  no  greater  than  the  upward  force  exerted  upon  it  by 
the  tendency  of  the  depressed  liquid  surface  to  straighten  out  into  a 
flat  surface,  the  needle  could  not  sink  in  the  liquid,  no  matter  how  great 
its  density.  If  the  water  had  wet  the  needle,  that  is,  if  it  had  risen 
about  the  needle  instead  of  being  depressed,  the  tendency  of  the  liquid 
surface  to  flatten  out  would  have  pulled  it  down  into  the  liquid  instead 
of  forcing  it  upward.  Any  body  about  which  the  liquid  is  depressed 
will  therefore  float  on  the  surface  of  the  liquid  if  its  mass  is  not  too 
great. ' ' 

If  the  needle  floats,  the  surface  is  turned  downward,  as  in  Fig.  3, 
where  the  resultant  of  the  parallelogram  of  adhesive  and  cohesive 
forces  lies  in  the  liquid ;  and  if  it  sinks,  the  surface  is  turned  up,  as  in 
Fig.  2,  where  the  resultant  lies  in  the  solid.  Therefore,  may  we  not  say 
that  if  we  can  draw  the  resultant  of  the  forces  of  cohesion  and  adhesion 
when  a  mineral  is  in  contact  with  water,  we  can  predict  whether  or  not 
it  is  floatable ;  for  if  the  resultant  lies  in  the  liquid  (Fig.  3)  it  will  float, 
and  if  it  lies  in  the  mineral  (Fig.  2)  it  will  sink. 

We  note  next  that  when  water  is  in  contact  with  quartz  the  result- 
ant lies  in  the  solid ;  when  it  is  in  contact  with  galena13  the  resultant 
lies  in  the  liquid.  We  can,  therefore,  separate  galena  from  quartz  by 
flotation.  I  believe  it  to  be  quite  possible  for  us  to  use  a  contaminat- 
ing substance  in  the  water  and  thus  vary  the  molecular  attractive 
forces  so  that  with  some  sulphides  the  resultant  lies  in  the  liquid  and 
with  other  sulphides  it  lies  in  the  solid.  This,  indeed,  has  been  done, 
and  I  believe  that  this  idea  is  essential  to  the  understanding  of  selective 
and  differential  flotation.  To  be  sure,  the  introduction  of  the  paral- 


and  quartz  are  here  supposed  to  be  in  such  condition  that  they 
are  typical  of  floatable  and  non-floatable  minerals. 


180  FLOTATION 

lelogram  of  forces  is  only  a  shift  from  one  series  of  unknowns  to  an- 
other, but  it  affords  a  means  of  stating  the  problem  accurately,  which  is 
the  first  step  in  a  solution. 

The  reader  here  exclaims:  "Oh  well,  you  are  talking  about  film- 
flotation?"  I  think  that  anyone  who  will  give  serious  thought  to  the 
above  demonstration  of  capillary  rise  and  depression  will  be  convinced 
that  there  is  nothing  but  film-flotation.14  All  flotation  depends  upon 
the  film.  If  a  piece  of  sulphide  is  brought  to  the  surface  by  a  bubble, 
it  is,  indeed,  riding  on  the  wall  of  a  hole  in  the  water,  the  only  differ- 
ence between  this  and  what  is  commonly  meant  by  film-flotation  being 
that  the  hole  is  a  sphere  with  finite  radius  while  in  *  film-flotation'  the 
surface  of  the  wall  has  an  infinite  radius. 

If  this  is  true,  we  go  too  far  afield  when  we  marshal  osmosis,  new- 
born gas,  static  charges,  etc.,  for  the  first  lesson  in  flotation. 

Many  writers  have  expressed  a  desire  to  discover  the  nature  of 
the  forces  that  cause  a  sulphide  particle  to  cling  to  a  bubble.  I  think 
their  desire  will  never  be  appeased,  for  there  is  no  such  adherence,  ex- 
cept in  so  far  as  there  is  a  slight  adhesion  of  the  liquid  film  to  the  min- 
eral as  it  rides  in  the  cavity  in  contact  with  the  wall  or  on  a  plane  sur- 
face. With  this  exception,  a  bubble  does  not  cling  to  a  sulphide  parti- 
cle in  a  flotation-cell  any  more  than  butter  clings  to  our  fingers  when 
we  carry  a  pound  of  it  from  the  store. 

What  has  been  observed,  and  not  properly  interpreted,  is  the  coa- 
lescence of  two  cavities,  one  of  which  is  filled  with  mineral  and  the 
other  with  air,  where  the  mineral  is  brought  to  rest  on  the  wall  of  the 
resulting  cavity  or,  perchance,  the  walls  of  the  two  cavities  do  not 
break  through  but  merely  cling  together. 

A  piece  of  submerged  galena  is  just  as  surely  surrounded  by  a  sur- 
face-tension liquid  film  as  is  the  air-bubble  or  submerged  greased 
needle.  If  this  is  not  plain  look  again  at  the  familiar  cross-section  of 
the  floating  needle,  Fig.  6.  That  the  film  extends  below  the  needle 
there  is  no  question,  and  it  is  just  as  sure  that  if  the  needle  were  sub- 
merged the  film  would  surround  it.  It  is  obvious  that  any  submerged 
solid  is  surrounded  with  a  liquid  film  when  the  resultant  lies  in  the 
liquid,  for  this  resultant  represents  an  inward  drawing  of  the  molecules 
that  causes  the  contractile  force  known  as  surface-tension. 

If  a  piece  of  quartz  impinges  against  the  wall  of  one  of  these  cav- 
ities and  has  not  sufficient  kinetic  energy  to  carry  it  through,  as  a  bul- 
let pierces  a  thin  board,  the  rise  of  the  liquid  about  it  and  the  contract- 


i4This  statement  applies  to  the  processes  now  in  operation,  not  the  original 
bulk-oil  method  of  Elmore. 


MOLECULAR    FORCES 


181 


ile  drawing  of  surface-tension  will  cause  it  to  retreat  directly  into  the 
liquid  just  as  surely  as  the  glass  tube  in  Fig.  4  is  pulled  into  the  water. 
If  it  has  sufficient  energy,  so  that  it  can  pierce  the  wall  where  it  first 
impinges  and  falls  on  the  wall  in  another  place,  it  will  likewise  be  cast 
out  of  the  cavity.  When  a  piece  of  galena  hits  the  wall  the  conditions 
are  entirely  different ;  for  the  galena  fills  a  cavity  that  has  walls  just 
like  those  of  the  bubble  and  what  happens  is  nothing  more  or  less  than 
the  coalescence  of  two  bubbles.  If  the  impact  is  very  slight  they  might 
only  cohere,  and  thus  give  the  appearance  of  a  mineral  grain  clinging 
to  the  bubble,  when  in  fact  it  is  the  bag  about  the  mineral  that  has  be- 
come attached. 

It  is  commonly  accepted  that  a  hole  in  water  filled  with  air  is  en- 
cased in  a  surface-tension  film ;  by  applying  the  principles  set  forth  by 
Millikan  and  Gale  one  sees  that  a  similar  encasing  film  exists  when  the 
hole  is  filled  with  either  a  greased  needle  or  galena.  In  the  first  case 


FIG.  6a 

there  is  a  wall  of  air ;  in  the  second,  a  wall  of  grease ;  and  in  the  third,  a 
wall  of  galena.15  In  every  case  the  resultant  of  cohesion  and  adhesion 
is  such  that  it  lies  in  the  liquid.  A  piece  of  glass  submerged  in  mercury 
would  be  surrounded  by  an  extremely  strong  film.  If  glass  is  sub- 
merged in  water  there  is  no  surface-tension  liquid  film. 

I  have  cited  an  instance  where  there  is  no  liquid  encasing  film  at 
all  (glass-water  interface)  and  one  where  the  film  is  excessively  strong 
(glass-mercury  interface) .  May  not  these  extremes  be  plotted  and  con- 
nected by  a  continuous  curve  with  points  to  show  the  tension  at  the 
solid-liquid  interface  of  various  combinations  of  substances?  Yes,  and 
more  than  that.  One  end  of  the  curve  might  represent  great  surface- 
tension  in  the  surface  of  the  solid  and  the  other  end  a  great  surface- 
tension  in  the  surface  of  the  liquid.  Fig.  6a  is  a  diagrammatic  sketch 


15Whether  or  not  galena  be  surrounded  by  a  film  of  adsorbed  air  or  grease 
does  not  concern  us  now. 


182  FLOTATION 

to  show  this.  The  surface-tension  of  the  glass-water  interface,  where 
the  resultant — arid  therefore  the  surface-tension — is  in  the  solid,  is 
placed  at  one  end  and  the  curve  passes  through  a  zero  surface-tension 
to  an  extreme  point  representing  tension  at  the  glass-mercury  inter- 
face. 

If  the  resultant  lies  in  the  solid  there  is  no  liquid  film,  but,  instead, 
a  surface-tension  solid  film,  and  the  surface-tension  would  plot  on  ao  in 
the  quadrant  xoz ;  while  if  the  resultant  is  in  the  liquid  there  is  a  liq- 
uid film  and  the  surface-tension  would  be  indicated  by  a  point  on  ob 
in  the  quadrant  woy.  It  seems  to  me  obvious  that  the  nori-flotative 
minerals  would  plot  to  the  left  and  the  flotative  minerals  to  the  right 
of  zw,  and  that  such  minerals  as  fluorite,  garnet,  and  calcite,  which 
have  been  described  as  at  times  inclined  to  float,  would  be  placed  very 
near  zw. 

Since  I  have  said  so  much  about  the  encasing  surface-tension  film, 
it  might  be  well  to  see  if  the  workers  in  colloid  chemistiy  take  cogni- 
zance of  this  sort  of  thing.  Indeed,  we  find  that  there  is  no  lack  of  pre- 
cedents. The  idea  of  films  around  small  particles  has  long  since  been 
accepted,  and  furthermore,  before  the  Wilfley  table  was  invented,  they 
knew  that  is  was  the  coalescence  of  these  films  that  caused  aggregation. 
I  quote  from  '  Colloid  Chemistry '  by  Ostwald,  page  88 :  "  Stress  was 
laid  upon  the  importance  of  these  envelopes  in  phenomena  of  conden- 
sation early  in  the  history  of  colloid  chemistry.  Thus,  J.  M.  van  Bem- 
melen  wrote  in  1888:  'I  think  it  possible  that  the  formation  of  the 
flakes  which  are  precipitated  in  a  liquid  is  dependent  upon  a  change  in 
the  surface-tension  of  the  liquid  membranes  surrounding  the  colloid 
particles,  of  such  type  that  these  membranes  between  the  particles  are 
torn  at  some  point,  thus  permitting  the  particles  to  form  aggregates.'  ' 

This  excellent  picture  of  aggregation  tempts  me  to  quote  more  of 
Ostwald 's  text,  but  we  must  leave  it  and  finish  the  high-school  book 
before  taking  up  a  more  advanced  work.  In  doing  this  let  us  make 
some  simple  tests.  Touch  the  round  end  of  a  glass  rod  to  the  surface 
of  water.  No  sooner  does  the  smallest  physical  point  come  in  contact 
with  the  water  than  the  water  seems  to  jump  to  the  rod  and  spread 
over  the  end  as  if  it  were  magnetized.  We  say,  that  is  to  be  expected, 
that  is  capillary  rise.  Observing  that  there  must  be  a  great  pressure 
exerted  upon  the  film  that  is  pulled  to  the  glass  rod  with  such  manifest 
energy,  we  explain  the  spreading  and  consequent  rise  in  the  terms  of 
John  Leslie,  who,  in  1802,  said :  * '  The  result  of  this  pressure  if  unop- 
posed is  to  cause  this  stratum  to  spread  itself  over  the  surface  of  the 
solid  as  a  drop  of  water  is  observed  to  do  when  placed  on  a  clean  hori- 


MOLECULAR    FORCES 


183 


zontal  glass  plate;  and  this  even  when  gravity  opposes  the  action,  as 
when  the  drop  is  placed  on  the  under  surface  of  the  plate." 

Since  this  plain  and  simple  reasoning  of  Leslie  ?s  is  credited  by 
Clerk  Maxwell  as  being  a  correct  explanation  of  the  rise  of  a  liquid  in 
a  tube  and,  further,  since  it  leads  up  to  the  same  conclusions  as  does  the 
'component  and  resultant'  method  of  Milikan  and  Gale,  we  feel  an 
added  security  and  proceed  with  a  similar  test  using  a  different  solid 
substance.  Let  us  take  for  this  test  a  fragment  of  galena  and  touch 
it  gently  to  the  surface  of  the  water.  Does  a  dimple  appear  immedi- 

Glass 


7 


FIG.  7 


FIG. 


ately  to  indicate  the  presence  of  a  membrance  that  is  resisting  rupture  ? 
Not  so.  The  water  jumps  to  the  galena  much  as  it  did  to  the  quartz, 
though  probably  not  so  vigorously.  We  argue  that  this  is  not  in  ac- 
cordance with  our  expectations ;  thereupon  we  repeat  the  test  and  make 
sketches. 

Fig.  7  shows  how  the  surface  of  the  water  is  elevated  to  wet  the 


Gloss 


— -^^--  Water 


FIG.  9 


=—-_z-~  Water 


FIG.  10 


glass  rod,  and  Fig.  8  shows  much  the  same  sort  of  phenomenon  when 
galena  is  used.  Though  badly  confused,  we  decided  to  carry  the  test 
one  step  farther.  To  do  this,  press  the  end  of  the  glass  rod  below  the 
natural  surface  of  the  liquid  and  also  allow  the  galena  to  float.  Fig. 
9  and  10  show  a  cross-section  through  the  contact  of  liquid  and  the  two 
solids. 

The  liquid  is  now  plainly  elevated  around  the  rod  and  depressed 
around  the  galena.  This  seems  perfectly  natural  and  satisfactory ; 
but  how  about  the  rise  of  the  liquid  in  Fig.  8  where  the  galena  seemed 
to  be  wetted  ?  It  is  nothing  more  nor  less  than  adhesion,  a  component 


184 


FLOTATION 


that  must  be  reckoned  with,  however  small  it  may  be,  as,  for  example, 
in  Fig.  3,  where  mercury  is  in  contact  with  glass.  Let  us  prove  that 
there  is  adhesion  between  mercury  and  glass.  To  do  this  we  will  take 
some  mercury  in  a  watch-glass  and  use  the  same  glass  rod.  If  we  watch 
closely,  as  we  lower  the  rod  to  meet  the  mercury,  we  can  see  that  the 
mercury  rises  a  little  around  the  end  of  the  rod  at  the  instant  they 
come  in  contact.  See  Fig.  11.  Upon  pulling  the  rod  away  it  is  plainly 
seen  that  there  is  adherence.  Having  performed  this  experiment  we 
may  go  into  the  mineralogy  laboratory  with  a  beaker  of  water  and  find 
that  any  one  of  a  dozen  minerals  taken  at  random  adheres  more  or  less 
firmly  to  water.  In  some  cases,  when  the  mineral  is  pressed  below  tne 
surface,  we  can  detect  capillary  rise  and  in  others  a  depression. 

Then  what  does  our  popular  term  'wetting*  mean?  It  can  mean 
nothing  more  than  absence  of  repulsion  unless  we  give  it  a  special  de- 
finition, as  some  physicists  have  done.  As  for  the  spreading,  Leslie, 
the  sage  of  more  than  a  century  ago,  in  speaking  of  adhesion  of  a  liquid 
to  a  solid  as  indicated  in  Fig.  7,  8,  and  11,  said :  "the  result  of  this  pres- 


Glass 


^7  Mercury 


FIG.  11 


ercury 


PIG.  13 


sure,  if  unopposed,  will  cause  the  liquid  to  spread."  When  the  adhes- 
ive force  is  sufficiently  in  excess  of  the  cohesive  force  the  liquid  will 
spread  indefinitely,  regardless  of  gravity,  until  the  thickness  is  such 
that  it  could  only  be  measured  in  terms  of  the  diameter  of  a  molecule. 
If  the  solid  body  attracts  the  liquid  strongly  enough  it  will  draw  every 
particle  of  it  as  near  as  possible  to  itself.  Thus  it  is  that  a  liquid 
spreads  over  certain  clean  surfaces.  But  such  perfectly  clean  sur- 
faces16 are  difficult  to  obtain  and  that  on  account  of  this  very  phenom- 
enon. Thus,  the  least  drop  of  oil  touching  a  glass  surface  spreads 
over  it  quickly  and  completely  changes  the  effect  of  adding  a  drop  of 


^'Mechanics,  Molecular  Physics,  arid  Heat.'    Millikan. 


MOLECULAR    FORCES  185 

water.  Such  deportment  needs  no  emphasis  to  impress  those  interested 
in  the  laws  relating  to  flotation. 

The  spreading  of  a  group  of  molecules  of  water  within  the  radius 
of  molecular  activity  of  the  glass  is  analagous  to  the  spreading  of  a 
ball  of  soft  putty  while  resting  on  a  plane  surface.  In  both  cases  the 
distortion  is  due  to  attraction;  in  the  first,  the  attraction  is  called 
molecular ;  in  the  second,  gravitational. 

But  analogies  do  not  satisfy  us ;  we  are  seeking  the  foundations  of  a 
new  arid  important  science,  and  there  will  be  opportunities  for  anal- 
ogies later.  Leslie  said  "if  unopposed."  We  shall  do  well  to  deal 
with  components  and  not  generalities.  We  are  reminded  therefore 


how  we  stated  above  that  in  some  cases,  when  the  mineral  was  pressed 
below  the  natural  surface  of  the  water,  we  could  detect  capillary  rise 
and  with  other  minerals  a  depression.  This  statement  must  be  consid- 
ered with  caution  lest  we  let  important  facts  slip  our  attention. 

Look  again  at  Fig.  4  and  5.  Shall  we  agree  that  in  contact  with  a 
perfectly  clean  piece  of  glass  the  surface  of  water  always  turns  up  and 
that  of  mercury  always  turns  down?  You  say,  Yes;  that  has  been 
proved.  Not  so;  and  here,  as  has  often  been  our  experience,  we  find 
that  we  have  to  unlearn  what  we  have  once  learned.  Let  us  place  a 
glass  rod  in  mercury  so  that  it  will  rest  in  a  position,  not  vertical  as  in 
Fig.  5,  but  in  an  inclined  position,  and  draw  the  components  of  ad- 
hesion and  cohesion  and  their  resultant.  See  Fig.  12. 

Now  we  know  that  the  surface  of  a  liquid  tends  to  adjust  itself  at 
right  angles  to  the  resultant  of  the  forces  acting  upon  it  and  that  if 
gravity  predominates  the  surface  is  horizontal.  But  let  us  consider  a 
group  of  molecules  at  O  so  small  that  the  molecular  forces  predomi- 
nate over  gravitational  forces.  We  have  the  force  of  adhesion  OE  act- 
ing at  right  angles  to  the  surface  of  the  glass  and  pulling  the  molecules 
to  it  and  the  cohesion  of  the  liquid  pulling  these  same  particles  in  the 
direction  of  OF.  The  resultant  of  the  two  forces,  OR,  is  the  force  to 
which  the  surface  assumes  a  position  at  right  angles,  and  since  OR 


186  FLOTATION 

lies  to  the  left  of  a  vertical  line  through  O  it  is  apparent  that  the  sur- 
face of  the  mercury  must  turn  up  to  meet  the  glass.  In  like  manner  it 
can  be  shown  that  the  mercury  turns  down  to  meet  the  glass  at  O1. 
Since  the  mercury  turns  down  at  0  in  Pig.  3  and  up  at  the  same  con- 
tact in  Fig.  12,  it  is  obvious  that  there  is  a  slope  of  the  glass  at  which 
the  mercury  would  stand  level.  It  may  seem  bold  to  draw  these  com- 
ponents so  freely  when  so  little  is  known  of  their  absolute  value.  It 
must  be  said  in  explanation  that  they  are  only  diagrammatic  and  that 
is  all  that  Milligan  and  Gale  intended.  It  is  a  fact,  however,  subject 
to  a  simple  ocular  demonstration,  that  mercury  does  turn  up  to  meet 
the  glass  at  0  and  down  at  O1,  Fig.  12.  The  point  to  be  made  is  that  in 
both  cases  the  resultant  lies  in  the  mercury,  even  though  the  mercury 
turns  up  to  meet  the  glass  as  does  water  against  glass  where  the  result- 
ant lies  in  the  solid,  and  that  the  slope  of  the  liquid  contact  must  be 
considered  only  in  connection  with  the  angle  at  which  the  mineral 
meets  the  original  surface  of  the  liquid.  The  elevation  of  the  mercury 
at  O  does  not  mean  that  the  sum-total  of  all  the  forces  tends  to  pull 
the  glass  down  as  does  water  pull  the  glass  in  Fig.  4,  for  we  must  re- 
member that  the  film  of  mercury  extends  entirely  around  and  under 
the  glass  and  that  it  tends  to  contract  and  reduce  its  distorted  surface- 
tension  film  to  a  minimum.  It  will  therefore  push  the  glass  upward  if 
the  downward  component  due  to  the  weight  of  the  glass  is  less  than  the 
upward  component  due  to  the  contractile  force  of  the  liquid.17  Briefly 
stated,  an  upturned  liquid  does  not  always  indicate  that  the  resultant 
turns  into  the  solid  as  one  would  conclude  from  a  study  of  Fig.  2.  By 
the  purely  theoretical  treatment  of  components  adopted  in  Fig.  12,  one 
can  show  that  the  surface  of  water  also  may  well  be  approximately 
horizontal  when  in  contact  with  glass. 

After  reaching  these  conclusions  by  merely  "reading  between  the 
lines "  of  a  most  elementary  physics  and  checking  them  by  laboratory 
tests,  it  is  interesting  to  note  that  a  more  advanced  text-book18  gives 
further  corroboration  in  the  recitation  of  a  "test  to  determine  the 
angle  of  contact  of  mercury  with  glass. ' ' 

An  inverted  spherical  flask,  as  shown  in  Fig.  13,  is  used.  The  quan- 
tity of  mercury  in  the  flask  is  adjusted  until  its  surface  in  contact  with 
the  glass  is  horizontal. 

Then  --  =  r  cos  (0  — )  >  where  0  is  the  angle  of  contact  sought, 


i7Here  the  principle  of  Archimedes,  namely,  loss  of  weight  due  to  dis- 
placed liquid,  is  not  taken  into  account. 
is'General  Physics,'  by  Edser,  p.  306. 


MOLECULAR    FORCES  187 

d  =  diameter  of  circle  of  contact  of  mercury  and  glass,  and  r  = 
radius  of  the  spherical  flask. 

Likewise  the  surface  of  water  would  be  about  as  shown  by  line  BB. 
Contamination  of  the  glass  or  liquid  might  well  give  surfaces  that  lie 
anywhere  between  the  two  mentioned.  This  might  be  called  a  reciproc- 
al method  for  determining  the  angle  of  contact ;  for  in  this  test  the  liq- 
uid surface  is  horizontal  and  the  solid  surface  is  inclined,  while  the 
angle  of  contact,  as  we  are  accustomed  to  thinking  of  it,  appears  with 
an  inclined  liquid  surface  against  a  vertical  solid  surface.  The  '  di- 
rect7 position  of  Fig.  13  appears  in  Fig.  14  where  A  A  and  CC  are  ver- 
tical. This  shows  the  same  angle  of  contact  in  a  position  more  famil- 
iar to  us. 

The  foregoing  shows  that  it  is  insufficient  to  say  that  the  liquid 


Mercury 
AT-—-^= 

PIG.  14 


C  — 


turns  up  or  down.  The  angle  of  contact  must  be  given ;  it  is  the  same 
regardless  of  the  slope  of  the  solid  surface.  For  example,  in  Fig.  12 
the  angle  of  contact  at  O  must  be  the  same  as  at  O1  and  again  the 
same  at  0  in  Fig.  3.  Again  the  actual  angle  of  contact  may  be  dis- 
torted by  the  weight  of  the  mass,  as  when  a  drop  of  mercury  rests 
on  glass. 

The  question  may  well  be  repeated :  Is  it  correct  to  speak  of  a  sur- 
face-tension film  of  mercury  against  glass,  and  if  the  term  is  correct,  do 
we  need  added  evidence  that  it  does  exist  at  the  mercury-glass  inter- 
face? 

In  our  first  conception  of  the  film  we  thought  only  of  the  upper  hor- 
izontal surface  of  a  liquid,  that  is,  the  liquid-air  interface  of  standing 
water.  We  then  extended  it  to  include  the  walls  of  a  submerged  air- 
bubble,  and  now  the  only  rational  application  of  film  or  membrane  is 
to  include  also  all  interfaces  where  there  is  surface-tension.  If  there 
is  a  solid-liquid  interface  in  which  the  resultant  turns  into  the  liquid, 
the  membrane  is  in  the  liquid,  and  if  the  resultant  turns  into  the  solid, 
the  membrance  is  in  the  solid.  It  is  of  the  utmost  importance  that 
we  add  contaminating  substances  to  the  mill-water  that  will  cause 
the  membrane  surrounding  the  grains  of  ore  (sulphides)  to  be  in  the 
liquid  and  simultaneously  cause  the  membrane  around  the  gangue  to 
be  in  the  solid.  Since  the  solid  membrane  is  an  intangible  sort  of  a 


188  FLOTATION 

thing  because  it  is  solid,  it  is  best  to  deal  with  its  antithesis:  the 
absence  of  a  liquid  membrane.  It  may  well  be  said  therefore  that 
when  the  flotation  metallurgist  has  contaminated  his  liquid  so  that 
there  is  a  liquid  membrane  around  the  ore  particles  and  none  around 
the  gangue,  he  has  mastered  the  first  step  in  his  process. 

The  liquid  film  must  not  only  surround  the  ore  particles,  but  it 
must  be  of  such  a  nature  that  it  will  rupture  at  the  point  of  contact 
with  an  impinging  air-bubble  and  thus  cause  coalescence ;  or  if  coales- 
cence does  not  take  place  the  films  must  cohere.  This  is  the  second 
step.  . 

Reference  to  another  simple  and  familiar  physical  experiment  may 
be  of  service  here  to  give  added  evidence  that  when  mercury  is  in  con- 
tact with  glass  the  membrane  is  in  the  liquid — a  state  quite  different 
from  water  in  contact  with  glass — and  aid  in  further  acquainting  us 
with  laws  second  to  none  in  their  application  to  flotation,  the  laws  of 
molecular  cohesion  and  adhesion. 

Take  two  conical  capillary  tubes,  a  and  fr,  Fig.  15.    Place  mercury 


FIG.  15 

in  a  and  water  in  b.  The  mercury  will  at  once  run  to  the  large  end  and 
the  water  as  quickly  to  the  small  end  of  the  respective  tubes.  The  mer- 
cury will  travel  to  the  larger  end  of  the  tube  even  though  it  be  slightly 
elevated.  In  doing  so,  it  decreases  its  surface  and  finally  reaches  the 
point  where  the  diameter  of  the  tube  is  sufficient  to  allow  it  to  assume 
the  form  of  a  sphere.  Such  conduct  is  possible  only  when  a  liquid  is 
surrounded  by  a  surface-tension  liquid  membrane.'  Here,  with  the 
mercury,  surface  energy  in  the  liquid,  after  its  well-known  manner, 
tends  to  reduce  the  amount  of  surface  to  a  minimum.  The  same  com- 
ponents exist  in  1),  but  they  are  of  different  magnitudes  and  are  such 
that  the  liquid  membrane  is  only  at  the  liquid-air  surface,  and  it  is 
obvious  that  it  is  reduced  by  a  movement  toward  the  small  end.  The 
concave  water  membranes  at  the  ends  are  similar  to  the  piston  of  a 
hydraulic  press,  and  the  liquid  is  drawn  in  the  direction  of  the  great- 
est force  per  unit  of  area.  If  we  assume  that  these  concave  surfaces 

2T 
are  hemispherical  it  is  obvious  from  the  formula,  P  =  — that  the 

drawing  forces  per  unit  of  area  toward  the  ends  are  inversely  as  the 
radii.  If  the  liquid  film  extended  entirely  around  the  water  such  an 
increase  in  total  surface  could  not  happen. 


(    MOLECULAR    FORCES  189 

"At  a  solid-liquid  interface  two  cases  are  therefore  possible — sur- 
face-tension in  the  same  sense  as  in  the  case  of  the  gaseous  bounding 
medium  may  appear  or,"  according  to  Wilhelm  Ostwald,  "we  may 
have  a  surface-tension  of  the  opposite  character.  In  this  the  (liquid) 
surface  does  not  tend  to  become  as  small  as  possible,  and  we  say  that 
the  solid  body  is  wet  by  the  liquid.  Mercury  on  glass  is  an  example 
of  the  first ;  oil  on  glass,  of  the  second.  When  the  surface  of  a  solid 
is  wet  by  a  liquid,  it  (the  solid)  acts  like  the  surface  of  a  liquid,  and 
therefore  seeks  to  become  as  small  as  possible." 

At  this  point  an  analogy  may  be  of  value,  not  as  a  proof  but  as  an 
aid  in  showing  how  the  deportment  of  mineral  grains  in  a  flotation-cell 
might  well  depend  on  whether  they  are  or  are  not  surrounded  by  a  liq- 
uid film. 

In  this  hypothetical  case,  we  grant  first  that  it  is  a  physical  fact 
that  glass  submerged  in  mercury  is  encased  in  a  liquid  membrane ;  that 
this  membrane  is  squeezing  the  glass  in  accordance  with  the  formula 

P=---}  in  the  same  manner  as  if  air  occupied  the  hole  in  the  mercury 

in  place  of  the  glass.  Second,  let  us  remind  ourselves  of  the  great 
'affinity'  of  mercury  for  gold.  This  affinity  or  capillarity19  is  well 
known  and  one  only  needs  to  be  reminded  that  gold  is  drawn  into  mer- 
cury20 in  the  same  manner  as  glass  is  drawn  into  water  to  see  that  they 
are  perfectly  co-ordinate. 

We  take  a  pulp  composed  of  mercury,  particles  of  gold,  and 
crushed  glass;  we  place  it  in  a  Callow  cell  and  blow  air  through  it. 
Can  you  conceive  of  the  gold  entering  or  even  clinging  to  an  air-bubble  ? 
No,  you  would  not  think  of  such  a  thing  any  more  than  you  would  of 
the  gold  in  the  amalgam  on  the  copper  plates  mysteriously  popping  to 
the  surface  and  parting  company  from  the  mercury.  But,  on  the  other 
hand,  consider  the  glass.  It  is  surrounded  by  a  liquid  membrane  of 
mercury.  If  this  membrane  comes  into  contact  with  the  membrane  of 
an  air-bubble  and  bursts  at  the  junction,  the  glass  will  be  squeezed 
out  of  its  little  sack  into  the  large  one  and  ride  securely  to  the  surface 
on  the  wall  of  the  resulting  bubble.  Thus  the  cell  would  produce  an 
overflow  of  glass  and  an  underflow  of  mercury  with  the  gold.  If  we 
replace  mercury  with  water,  glass  with  galena,  and  gold  with  quartz, 
and  adjust  the  detail  by  means  of  a  contaminating  substance,  we  af- 


using  'affinity'  and  'capillarity'  I  am  only  attempting  to  use  terms 
that  we  have  all  used  when  discussing  amalgamation. 

soThomas  T.  Read,  Trans.  A.  I.  M.  E.,  Vol.  37,  says  that  amalgamation  is  a 
physical  rather  than  a  chemical  process;  that  the  surface-tension  of  mercury 
draws  the  gold  beneath  the  surface. 


190  FLOTATION 

ford  a  complete  and  perfect  transfer  from  a  hypothetical  to  an  actual 
operating  flotation-cell.  Unfortunately,  too  many  of  us  have  con- 
cerned ourselves  so  much  with  detail — the  contaminating  substances, 
etc. — that  we  have  .failed  to  grasp  the  fundamental  idea.  Electrolytes, 
static  charges,  osmotic  pressure,  and  much  of  the  researches  of  recent 
workers  in  physical  and  colloid  chemistry  will  all  have  their  places  in 
the  science  of  flotation  after  the  foundation  has  once  been  laid. 

Archimedes  was  interested  only  in  the  mass  per  unit  of  volume, 
Leslie  in  the  manner  in  which  the  molecular  forces  of  substance  af- 
fected an  unlike  substance.  Since  the  range  of  action  of  molecular 
forces  is  so  very  small  it  is  obvious  that  only  those  molecules  at  the 
surface  could  be  sufficiently  close  to  another  substance  to  effect  it. 
We  are  interested,  therefore,  in  the  forces  at  the  common  surface  of 
two  substances.  In  this,  our  position  is  the  same  as  that  of  the  chemist. 
Bigelow21  says,  "more  and  more  we  are  realizing  that  the  conditions  in 
contact  surfaces  often  play  the  decisive  role  in  important  processes. ' ' 

I  have  tried  to  expose  the  fallacy  that  mineral  particles  adhere  to 
impinging  bubbles ;  as  an  alternative,  I  have  advanced  a  theory  involv- 
ing coalescence,  this  being  more  in  accord  with  scientific  ideas.  We 
are  familiar  with  the  coalescence  of  two  soap-bubbles,  but  have  much 
to  learn  concerning  the  coalescence  of  two  films  when  one  of  them  sur- 
rounds a  solid.  Here  I  would  recommend  a  study  of  boiling  in  the  vol- 
ume on  'Heat'  in  the  'Text  Book  of  Physics'  by  Poynting  and  Thomp- 
son. It  teaches  that  the  bubbles  which  carry  the  steam  to  the  surface 
of  a  liquid  do  not  rise  from  points  at  random,  but  from  definite  points 
or  particles  of  foreign  matter  that  form. a  boundary  of  the  liquid. 
There  must  be  a  nucleus  in  the  shape  of  a  minute  bubble  into  which 
the  steam  passes.  As  evaporation  proceeds,  the  bubble  grows  and  fin- 
ally breaks  away,  always  leaving  a  small  portion  behind  as  a  nucleus, 
just  as  part  of  the  neck  of  a  drop  of  water  is  left  when  the  drop  breaks 
off  from  a  surface.  Some  substances  carry  a  great  many  nuclei  while 
others  are  barren.  A  beaker,  thoroughly  cleansed  in  hydro-fluoric 
acid,  is  so  barren  of  nuclei  that  water  can  be  raised  several  degrees 
above  the  boiling  point  without  boiling  taking  place.  A  piece  of  flint 
immersed  in  a  liquid  was  alive  with  bubbles  over  its  entire  face  until 
broken  in  two,  when  no  steam  was  given  off  from  the  freshly  formed 
surface.  The  introduction  of  iron  filings  caused  rapid  ebullition.  Sub- 
stances over  which  water  is  most  reluctant  to  spread,  that  is,  those 
solids  which  show  the  least  adhesion  for  water,  furnish  the  greatest 


si'Theoretical  and  Physical  Chemistry,'  p.  247. 


MOLECULAR    FORCES 


191 


number  of  nuclei.  One  paragraph  from  a  paper  by  Lord  Rayleigh,22 
where  he  discusses  'Liberation  of  Gas  from  Super-saturated  Solu- 
tions, '  is  sufficient  to  show  the  close  relation  between  boiling  and  flota- 
tion. He  says:  "It  seems  to  me  that  Tomlinson  was  substantially 
correct  in  attributing  the  activity  of  non-porous  surfaces  to  imperfect 
adhesion.  We  have  to  consider  in  detail  the  course  of  events  when  a 
surface,  for  example,  of  glass,  is  introduced  into  the  liquid.  If  the  sur- 
face be  clean,  it  is  wetted  by  the  water  advancing  over  it,  whether 
there  be  a  film  of  air  condensed  upon  it  or  not,  and  no  gas  is  liberated 
from  the  liquid.  But  if  the  surface  be  greasy,  even  in  a  very  slight 
degree,  the  behavior  is  different."  In  another  book23  we  learn  that 
"metal  turnings  depress  the  boiling-point  because  their  molecular  at- 
traction for  water  is  less  than  that  of  glass. ' ' 

We  have  ample  evidence,  therefore,  that  solids,  like  fresh  quartz 
over  which  water  spreads  freely,  do  not  carry  nuclei  of  air,  while  sol- 
ids, like  galena  over  which  water  does  not  spread  freely  on  account  of 
adhesion,  do  have  small  bubbles  attached  to  them  while  submerged  in 
water.  For  an  extreme  case  where  air  nuclei  would  be  present,  we 
might  suppose  a  glass  sphere  to  be  submerged  in  mercury.  As  it 
passes  below  the  surface  with  its  angle  of  contact  of  140°,  it  would  ap- 
pear as  shown  in  Fig.  16. 


FIG.  16 


FIG.  17 


With  the  disappearance  of  the  waist  at  a,  the  film  closes  around 
an  air  nucleus.  A  small  quantity  of  air  would  thus  be  carried  down 
and  if  the  mercury  were  transparent,  one  could  see  an  air-bubble  at- 
tached to  the  glass.  A  fresh  piece  of  glass  in  water  would  not  do  this, 
for  the  water  would  close  over  it  as  shown  in  Fig.  17.  But  we  do  not 
have  to  go  so  far  afield  to  account  for  attached  air-bubbles.  The  sur- 
face of  all  minerals  contains  depressions  and  it  would  be  impossible  for 
them  to  pass  from  air  to  water  without  some  of  the  air  residing  in  the 
depressions  being  carried  below  the  surface.  Whether  or  not  the  air 


^Philosophical  Magazine,  Vol.  48,  1899. 
23'Theory  of  Heat.'    Preston. 


192  FLOTATION 

is  held  in  place  depends  on  the  adhesion  of  water  and  mineral.  If 
adhesion  is  less  than  cohesion  of  the  liquid  molecules,  the  surface-ten- 
sion film  will  pass  around  the  air  nuclei  and  hold  them  in  place,  but  if 
adhesion  is  great  the  water  will  spread  over  the  entire  surface  of  the 
mineral  and  ultimately  release  the  air  bubbles.  The  application  of 
these  principles  to  flotation  is  simple :  minerals  with  the  least  adhesion 
for  water  will  retain  the  greatest  number  of  small  bubbles ;  these  bub- 
bles are  inflated  by  gases  expelled  from  the  solution  and  finally  an 
air-bubble  in  its  passage  impinges  against,  and  coalesces  with,  the 
attached  bubbles  and  the  mineral  is  carried  to  the  surface  by  the  re- 
sulting bubble,  which  is  inflated  with  air  and  expelled  gas.  I  wish  to 
express  my  gratitude  to  Dr.  Joel  H.  Hildebrand  for  his  critical  reading 
of  these  notes  and  for  his  assistance  during  the  seminar  in  'Colloids 
and  Surface  Tension'  at  the  University  of  California.  Also  I  wish 
to  thank  H.  M.  Parks  and  Ira  A.  Williams  of  the  Oregon  School  of 
Mines  for  their  co-operation. 


THE  NUMBER  OF  MEN  NECESSARY  for  the  operation  of  large  flotation 
machines  is  remarkably  small.  At  the  Inspiration  plant,  one  operator 
supervises  four  sections  of  flotation  machines.  Two  Mexican  helpers 
assist  him  in  washing  the  bottoms,  thus  insuring  a  free  passage  of  air 
through  the  porous  medium.  At  the  prevailing  high  prices  of  Ameri- 
can and  Mexican  labor,  this  means  an  expense  of  somewhat  more  than 
1.5c.  per  ton  of  ore  treated.  The  total  expenses  representing  flota- 
tion proper  were  as  follows  for  the  months  of  March,  April,  and  May, 
1916: 

Cents  per  ton 

Labor    1.62 

Oils    1.65 

Other  supplies    0.35 

Power    2.14 

Total    5.76 

The  subsequent  table  treatment  of  the  flotation  tailing,  the  filtering 
of  the  concentrate,  and  other  operations  connected  with  the  process 
of  concentration,  belong  more  or  less  to  flotation  treatment,  and 
their  expense  should  also  be  considered  when  the  cost  of  the  flota- 
tion process  is  to  be  calculated.  The  total  milling  cost,  exclusive  of 
crushing  and  grinding,  has  been  for  the  past  few  months  in  the  neigh- 
borhood of  20  cents.  When  the  cost  of  crushing  and  grinding  is 
included,  the  cost  is  about  40c.  per  ton  of  ore.  Royalties  for  the  use 
of  the  flotation  process  are  not  included  in  any  of  these  cost  figures. 
—Rudolf  Gahl,  Trans.  A.  I.  M.  E. 


THE    ARMOR    IN   FLOTATION  193 

THE  ARMOR  IN  FLOTATION 

By  WILL  H.  COGHILL 
(Written  especially  for  this  volume) 

As  the  man  of  science  takes  a  beam  of  light  and  passes  it  through 
a  crystal  prism,  and  it  comes  out  on  the  other  side  of  the  prism  broken 
up  into  its  components,  so  we  must  take  each  effect  in  notation  and  re- 
solve it  into  a  'spectrum'  to  reveal  the  cause. 

It  has  pleased  us,  from  the  start,  to  speak  of  a  pregnant  froth  as 
'armored.'  By  this  expression  we  convey  the  idea  of  greater  stability 
on  account  of  solid  constituents.  Are  we  justified  ? 

At  the  beginning  it  is  necessary  to  have  in  mind  the  exact  physical 
relation  of  the  film  to  the  mineral  grains.  In  the  absence  of  facts  sub- 
ject to  ocular  verification  I  will  state  what  this  relation  should  be  when 
it  is  the  natural  effect  of  causes  as  I  understand  them.  I  believe  that  a 
froth  gets  its  load  from  two  sources :  first,  from  grains  wholly  or  partly 
surrounded  while  in  bulk-water  with  liquid  films  which  feed  the  bub- 
bles by  coalescence,  and  second,  from  mineral  grains  which  become 
entrapped  at  the  surface  of  bulk-water,  between  the  ascending  bubble 
and  the  lower  layer  of  the  froth.  The  chief  constituents  of  the  first 
are  sulphides,  of  the  second,  gangue  or  at  least  minerals  on  which 
water  spreads  freely,  and  appear  as  shown  in  Fig.  1.  The  first,  if 


FIG.   1.      FROTH   LADEN   WITH   QUARTZ 

wholly  non-wetted,  ride  upon  the  surface  of  the  froth  just  as  galena 
rides  the  surface  of  bulk-water  in  a  H.  E.  Wood  machine,  and  further, 
they  are  on  the  outer  surface,  being  the  solid  residue  from  perished 
bubbles.  If  partly  non- wetted  (perchance  these  constitute  a  great  por- 
tion of  the  floatable  sulphides),  the  dry  spots  would  tend  to  prevent 
sinking  while  water  would  spread  on  the  remaining  portion.  A  hy- 
pothesis involving  a  partly  wetted  surface  is  justified  by  the  results  of 
physical  measurements.  I  refer  to  the  work  of  Dr.  Huntington,  who 
found  that  the  angle  of  contact  of  dark  blende  on  a  principal  cleavage 
face  was  53°  while  on  another  cleavage  of  the  same  specimen  it  was 


194 


FLOTATION 


69 °.1    Again,  a  part  of  the  surface  of  the  mineral  might  be  old  while 
another  part  is  new — formed  in  a  ball-mill,  for  example. 

In  a  recent  article2 1  called  attention  to  the  way  in  which  like  float- 
ing objects  are  attracted  to  each  other.  Let  us  take  the  case  of  two 
pieces  of  galena  floating  011  bulk-water  to  find  the  numerical  value  of 
this  force  of  attraction,  that  is,  the  strength  of  the  armor.  They  ap- 
pear as  shown  in  Fig.  2. 


-_--_  --.  ~*^      ~i  O-O2/  c.m. 

<— 

^^™ 

7^>x 

/^L  —  - 

a.    ~~   —    —    ~ 

H  ~  ~  _a 

b 

—     —     ~b 

— 

FIG.    2.      BULK-WATER  LADEN   WITH   GALENA 


The  side  pressure  above  the  line  aa  is  that  of  the  atmosphere  and 
the  same  at  all  points.  The  pressure  below  bb  is  that  of  the  liquid  in 
equilibrium.  The  unbalanced  force  then  must  lie  between  aa  and  bb. 
We  know  that  at  all  points  in  the  free  surface  of  a  liquid,  where  it  is 
plane,  the  pressure  is  the  same  and  is  that  of  the  atmosphere,  increas- 
ing at  the  rate  of  one  gram  per  square  centimetre  for  every  centi- 
metre in  depth. 

Assume  that  the  pieces  of  galena  have  a  length  of  one  centimetre 
with  the  cross-section  shown  (about  65-mesh)  and  that  aa  and  lb  rep- 
resent traces  of  horizontal  planes  containing  the  contacts  of  the  three 
phases.  The  area  subjected  to  the  unbalanced  force  is  about  0.01  cm. 
X  1  cm.  —  0.01  sq.  cm.  The  average  depth  is  about  0.02  cm.  The  total 
unbalanced  hydrostatic  pressure  is, 

0.01  X  0.02  =  0.0002  gm.  or  0.2  mg. 

It  seems  apparent  then  that  the  unbalanced  hydrostatic  pressure 
(0.2  mg.)  is  such  a  small  part  of  the  tensile  strength  of  the  film  (70 
mg.)  that  the  armor  effect  from  this  cause  is  negligible.3 

The  same  method  of  calculation  can  not  be  applied  to  sulphides  on 
curved  liquid  films,  but  I  believe  that  any  effect  from  a  similar  cause 
can  be  ignored.  There  is,  however,  an  unquestioned  armor  effect  due 
to  the  arching  of  a  solid-liquid  mixture  with  the  concave  (upward) 


iTrans.  Faraday  Society,  Vol.  1,  1915. 
2Colorado  School  of  Mines  Magazine,  January  1917. 

sThe  drawing  (Fig.  2)  is  only  an  approximation  of  conditions  as  they  exist 
on  bulk-water,  but  is,  I  believe,  sufficiently  correct  to  justify  the  conclusion. 


THE    ARMOR   IN  FLOTATION  195 

surface  of  the  film  and  the  containing  walls  of  the  flotation  machine 
for  skewbacks.  The  measure  of  this  effect  must  be  left  to  conjecture. 

Quartz  (gangue)  in  the  froth  must  next  be  considered  to  see  if  it 
has  a  stabilizing  effect.  At  first  thought  it  may  seem  that  quartz  goes 
into  the  froth  in  opposition  to  the  laws  of  cause  and  effect.  But  this 
view  is  wrong,  and  further,  the  cause  producing  this  effect  is  perfectly 
apparent.  Too  little  thought  has  been  given  to  this  phase  of  flotation. 
The  pyro-metallurgist  gives  his  chief  attention  to  the  slag  and  lets  the 
metals  take  care  of  themselves.  In  flotation  we  have  given  all  our 
thought  to  the  sulphides.  Let  us  consider  the  gangue  for  a  moment. 
It  is  indeed  a  truism  that  anything  in  the  category  from  horse-shoes 
to  diamonds  can  be  collected  in  a  froth,  if  sufficiently  small,  so  that  the 
force  of  gravity  is  negligible  as  compared  with  the  molecular  forces 
of  cohesion  and  adhesion.  Please  picture  the  froth-covered  pulp  in  ag- 
itation. A  rising  bubble  about  to  emerge  and  pass  into  the  froth  is 
separated  from  the  froth  by  only  a  thin  stratum  of  pulp,  that  is,  by 
water  with  a  uniform  mixture  (if  the  gangue  is  not  flocculated)  of  all 
the  constituents  of  the  ore.  In  an  instant  the  films  come  together  and 
a  portion  of  the  solids  are  entrapped.  Being  thus  entrapped,  it  is 
contrary  to  the  laws  of  nature  for  galena  to  escape  the  clutches  of  the 
liquid  film,  and  the  exit  for  the  quartz  is  a  restricted  one,  as  will  be 
shown  later.  For  galena  is  repelled  from  the  liquid  by  the  film  and 
obliged  to  ride  upon  it  and  quartz  is  drawn  into  the  film  and  made 
fast  between  the  two  surfaces.  There  is  no  exception.4 

It  is  impossible  to  practice  flotation  without  entrapping  a  portion 
of  the  solids;  these  might  consist  of  mineral  or  gangue  in  the  condition 
of  either  galena  or  quartz,  or  any  of  the  possible  combinations;  but 
whatever  the  condition,  they  must  conduct  themselves  as  one  or  the 
other.  It  is  not  at  all  unlikely  that  some  of  the  sulphides  contributing 
toward  a  rich  concentrate  are  entrapped  grains  in  the  condition  of 
quartz  and  therefore  held  in  the  film  as  shown  in  Fig.  1. 

Do  such  grains  add  tensile  strength  to  the  film?     Having  proved 


4This  cannot  be  over-emphasized.  All  minerals  when  classified  according 
to  flotative  properties  (where  liquid  and  air  are  the  fluid  phases)  come  under 
one  of  two  separate  and  distinct  heads;  they  either  exert  an  adhesive  force 
greater  than  a  certain  minimum  so  that  the  liquid  spreads  upon  them  with 
no  ultimate  increase  of  surface  energy,  or,  an  adhesive  force  less  than  this,  so 
that  their  submergence  increases  the  area  of  the  surface-tension  film  and 
therefore  the  surface  energy.  In  short,  a  liquid  surface-tension  film  is  either 
absent  or  present  at  a  solid-liquid  interface.  Where  it  is  absent  the  liquid 
tends  to  include  the  mineral.  Where  it  is  present  the  liquid  tends  to  exclude 
the  mineral.  I  have  symbolized  the  former  by  'quartz'  and  the  latter  by 
'galena.'  What  I  have  said  applies  to  vesicles  of  water  inflated  with  air  (a 
bubble)  as  well  as  to  bulk-water. 


196  FLOTATION 

the  inefficacy  of  forces  arising  from  surface  configuration  in  the  one 
case  (Fig.  2)  it  can  be  dismissed  in  this;  but  a  scrutiny  of  Fig.  1 
brings  to  mind  the  popular  demonstration  in  physics  showing  the  enor- 
mous force  with  which  two  discs  are  pulled  together  by  a  drop  of 
water.  The  demonstration  runs  about  as  follows: 

"It  is  a  matter  of  common  experience  that  the  hairs  of  a  paint- 
brush cling  together  when  the  brush  is  withdrawn  from  the  water. 
The  reason  is  obvious;  water  clings  to  the  hairs,  and  the  free  surface 
of  the  liquid  tends  to  contract  and  pull  them  together.  The  force  is 
much  greater  than  the  force  of  surface-tension. 

"Let  Fig.  3  represent  the  side-view  of  two  plates  with  a  drop  of 


FlG.   3.      PARALLEL  PLATES  WITH  A  DROP  OF  WATER  BETWEEN    THEM 

water  between  them.  The  water  spreads  out  into  a  circular  disc  of 
considerable  area.  Let  R  be  the  radius  of  the  flattened  drop ;  d  the 
distance  between  the  plates,  equal  2r;  and  let  T  equal  surface-tension 
of  the  liquid.  Then  the  total  force  F  urging  the  plates  together  is, 


"If  the  surfaces  are  true  planes,  the  discs  will  approach  each  other 
until  d  becomes  exceedingly  small,  and  the  force  exerted  may  be  suf- 
ficient to  fracture  them. ' ' 

This  formula  cannot  be  applied  to  the  problem  before  us  because 
the  conditions,  so  much  alike  in  some  respects,  are  so  different  in  others 
that  the  conclusions  would  be  misleading.  An  acquaintance  with  the 
method  of  derivation  is  necessary  in  order  to  appreciate  this.  The 
water  between  the  discs  is  under  a  dilational  strain  due  to  its  tendency 
to  spread.  The  water  between  the  mineral  grains  in  Fig.  1  is  also 
under  a  dilational  strain,  but  the  strain  in  this  case  is  due  to  the 
weight  of  the  column  of  water  reaching  along  the  films  to  the  surface 
of  bulk-water.  It  is  as  if  the  water-filled  opening  between  them  were 
connected  to  a  water-surface  through  a  suction-pipe.  There  is  an 
interesting  analogy  in  a  discussion  of  regelation  that  reads  as  follows : 
"When  two  blocks  of  ice  are  placed  loosely  together  so  that  the  super- 
fluous water  which  melts  from  them  may  drain  away,  the  remaining 
water  draws  the  block  together  with  a  force  sufficient  to  cause  the 
blocks  to  adhere."  If  the  water  were  drained  away  from  the  ice 


THE    ARMOR    IN    FLOTATION  197 

through  a  draught-tube  the  analogy  would  be  perfect.  Having  thus 
stated  the  problem,  the  calculation  is  simple.  Assume  that  the  vertical 
length  of  this  draught-tube  is  25  cm.  (about  10  in.)  the  depth  of -the 
froth,  using  grains  of  the  same  dimension  as  before,  and  we  have  as  a 
difference  between  inside  and  outside  pressure  due  to  the  weight  of 
water  sustained, 

0.021  X  25  =  0.525  gm.,  or  525  mg. 

while  as  before  the  tensile  strength  of  the  surface-tension  film  (two 
surfaces)  is  about  70  mg.  A  temporary  armor,  at  least!  I  say  "tem- 
porary" because  the  rough  surface  presented  in  Fig.  1  is  not  one  of 
minimum  potential  energy*  If  anything  tends  to  disturb  the  equilib- 
rium it  must  be  considered.  There  is  one  thing.  I  refer  to  the  weight 
of  the  column  of  water  sustained  and  believe  that  it  would  tend  to  slip 
the  quartz  grains  along  the  film  to  bulk-water.  As  a  result  the  skew- 
backs  for  the  arch  would  be  continually  dropping  back  into  the  water, 
(see  Fig.  4),  at  a  rate  depending  on  viscosity  and  other  factors.  The 


PIG.    4.       A   BUBBLE    SPILLING    QUARTZ    BACK    INTO   THE   WATER 

weight  of  the  grains  themselves  would  also  tend  to  produce  this  slip- 
ping. As  for  viscosity,  we  know  that  quartz  would  drop  back  faster  in 
a  film  of  low  viscosity  and  that  viscosity  decreases  with  rise  of  tempera- 
ture. Heat  should  therefore  improve  the  grade  of  concentrate.  While 
there  might  well  be  causes  which  would  neutralize  this  effect  it  is  in- 
teresting to  associate,  in  this  connection,  a  paragraph  from  Dr.  Gahl's 
paper5  that  reads  as  follows :  i  i  How  can  we  raise  the  grade  of  our  con- 
centrates— that  is,  reduce  the  percentage  of  insoluble  matter  contained 
in  them — without  entailing  additional  copper  losses?  We  know  from 
laboratory  experiments  that  this  can  be  done  by  expensive  methods, 
for  instance,  by  heating  the  solutions."  Would  not  heating  the  froth 
only,  with  steam-coils,  effect  the  same  advantage  at  much  less  cost  ? 

By  the  use  of  fundamental  principles  of  physics  I  have  adduced 
considerations  that  are  in  accord  with  colloid-chemistry,  namely,  solids 
armor  a  froth.  To  justify  this  conclusion,  I  quote  from  W.  D.  Ban- 


.  A.  I.  M.  E.,  Sept.  1916,  p.  1675. 


198  FLOTATION 

croft:6  "We  cannot  get  a  froth  with  a  pure  liquid  and  air.  There 
must  be  present  a  third  substance  in  colloid  solution."  Again,  Mr. 
Bancroft  says  that  we  call  a  phase  'colloidal'  when  it  is  sufficiently  sub- 
divided, not  limiting  ourselves  definitely  as  to  what  degree  of  subdi- 
vision.7 He  states  that  a  sufficiently  subdivided  phase  stabilizes  a 
froth.  In  so  doing  he  has  stated  the  effect.  I  have  tried  to  point  out 
the  cause. 

If  the  impression  given  by  Fig.  1  is  that  what  I  have  said  about 
stabilizing  causes  applies  only  to  coarse  mechanical  suspensions,  that 
is,  where  the  diameter  of  the  discontinuous  phase  is  greater  than  the 
thickness  of  the  film,  it  should  be  made  clear  that  suspensions  of  all 
degrees  of  dispersion  (diameter  of  the  solid)  are  included.  Wolfgang 
Ostwald 's8  discussion  of  internal  friction  of  suspensoids  justifies  this 
conclusion.  He  says:  "It  may  be  regarded  as  typical  of  suspensoids 
that  their  viscosity  is^but  slightly  greater  than  that  of  their  pure  dis- 
persion mediums.  It  must  be  remembered,  however,  that  this  is  true 
only  when  such  systems  are  dilute.  In  concentrated  form  the  mass  ot1 
the  disperse  solid  phase  may  predominate  over  that  of  the  dispersing 
medium,  as  when  powders  are  merely  moistened  so  as  to  be  coated  by 
a  thin  but  continuous  liquid  membrane.  Such  systems  may  be  so  vis- 
cid that  their  properties  approximate  those  of  solids.  We  need  but 
recall  how  moist  sand  may  be  cut  into  slices,  and  the  rigidity  of  the 
scales  and  crusts  of  dried  colloid  metals.  From  this  it  follows  that  with 
increase  in  concentration  the  viscosity  of  a  suspensoid  rises  very  slowiy 
at  first,  but  very  suddenly  and  greatly  at  high  concentrations."  What 
I  have  indicated  in  Fig.  1  is  equivalent  to  the  'slice'  mentioned 
by  Ostwald.  It  is  not  necessary  for  the  armor  to  extend  over  the  whole 
surface  of  the  froth  in  order  for  it  to  have  a  stabilizing  effect. 

When  the  discontinuous  phase  has  such  a  high  degree  of  dispersion 
that  the  conditions  approach  those  of  a  molecular  solution  (soap  in 
water  is  an  example)  there  is  a  new  set  of  forces  to  be  considered.  This 
has  been  described  and  called  '  adsorption. ' 

One  has  only  to  shake  finely  crushed  ore  in  a  test-tube  with  water 
to  see  that  the  solids  lend  persistence  to  the  bubbles  though  in  some 
cases  the  bubbles  taken  collectively  may  not  be  sufficiently  voluminous 
to  constitute  what  is  ordinarily  styled  a  froth.  There  is  nothing  new 
about  this.  T.  K.  Rose9  says:  "Losses  in  amalgamation  are  also  caused 


<$Met.  d  Chem.  Eng.,  June  1,  1916,  p.  634. 
7'The  Flotation  Process,'  by  Megraw,  p.  28, 
s'Handbook  of  Colloid  Chemistry,'  by  Ostwald,  p.  146. 
9'Metallurgy  of  Gold,'  by  T.  K.  Rose,  p.  207. 


THE    ARMOR    IN   FLOTATION  199 

by  greasy  substances  contained  in  some  ores,  such  as  the  powdered  hy- 
drated  silicates  of  magnesia  and  of  alumina,  which  cause  frothing." 

Rose  says  'greasy.'  This  would  indicate  that  the  galena  type  of 
mineral  is  the  greater  stabilizer.  On  the  other  hand  Gahl10  thinks 
that  the  frothing  characteristics  follow  the  tailing-pulp.  We  must, 
someday,  learn  more  about  this.  Taggart  and  Beach11  are  doubtless 
justified  in  their  statement  that  "the  formation  of  a  scum  of  floated 
sulphide  increases  the  stability  of  the  float,"  but  when  they  say,  in  dis- 
cussing adsorption  and  surface  tension,  "On  philosophical  grounds 
it  is  impossible  to  consider  that  a  real  physical  discontinuity  occurs 
at  the  boundary  between  two  media.  In  other  words  there  must  be 
a  very  thin  layer  of  transition  in  which  there  is  a  rapid  but  continuous 
change  in  the  concentration  of  the  components, ' '  they  are  perpetuating 
an  early  conception  that  has  been  more  befogging  to  me  than  anything 
I  have  read  relating  to  this  subject.  After  being  so  perplexed  by  the 
frequent  recurrence  of  this  statement  in  the  various  texts,  it  was  in- 
deed a  delight  to  read  from  the  pen  of  Irving  Langmuir  in  a  paper12 
that  impresses  me  as  epoch-making  in  the  studies  of  surface-tension, 
as  follows:  "The  surface  of  a  solid  (or  liquid),  therefore,  does  not 
contain,  as  is  usually  assumed,  a  transition  layer,  consisting  of  several 
layers  of  atoms  or  'molecules,'  in  which  the  density  varies  by  con- 
tinuous gradations  from  that  of  the  solid  to  that  of  the  surrounding 
gas  or  vapor.  Instead  we  find  that 'the  change  from  solid  to  empty 
space  is  most  abrupt.  In  a  sense,  the  re-arrangement  of  the  atoms,  in 
the  surface  layer,  causes  this  layer  to  assume  the  character  of  a  transi- 
tion layer,  but  the  density  of  the  packing  of  the  atoms  in  this  layer  is 
undoubtedly  greater  than  in  the  body  of  the  solid,  so  that  there  can 
be  no  gradual  change  in  density  from  that  of  the  solid  to  that  of 
space."  Mr.  Langmuir 's  conception  impresses  me  as  consistent,  the 
other  not. 

There  is  yet  another  thing  to  be  said  about  a  bubble  with  grains 
deposited  between  the  films  as  shown  in  Fig.  1,  to  wit.  the  space  be- 
tween the  grains  is  a  repository  for  water.  A  wet  froth  would  there- 
fore accompany  a  low-grade  concentrate.  Indeed  this  seems  to  be 
in  accord  with  observation.  For  example,  "Toward  the  tailing  end 
of  the  flotation  machines,"  says  Dr.  Gahl,  "most  of  this  dark  ma- 
terial has  disappeared  and  the  froth  is  lighter  and  of  a  more  watery 
nature. ' ' 


l.  A.  I.  M.  E.,  Sept.  1916,  p.  1680. 
nBull.  A.  I.  M.  E.,  Aug.  1916,  p.  1382. 

^'Constitution  and  Fundamental  Properties  of  Solids  and  Liquids/  Journal 
of  American  Chemical  Society,  Nov.  1916,  p.  2249. 


200  FLOTATION 

ELECTRO-STATICS  AND  FLOTATION* 

BY  JAMES  A.  BLOCK 

Somewhat  over  a  year  ago  it  was  first  announced*  to  the  metallur- 
gical world  that  certain  investigators  working  on  flotation  were  study- 
ing the  functions  of  the  electro-static  charges  observed  on  the  surfaces 
of  the  mineral  particles  and  of  the  bubbles.  It  was  suggested  that 
these  charges  might  in  themselves  account  for  flotation.  In  fact  one 
writer,  Thos.  M.  Bains,  Jr.,  excluded  all  other  explanation  of  flota- 
tion phenomena.1  Much  work  has  been  done  in  that  direction  dur- 
ing the  year  past,  but  since  little  has  been  written  concerning  it,  other 
theorists  have  recognized,  criticized,  or  trampled  upon  the  so-called 
electro-static  theory  to  their  heart's  content.  Generally  speaking, 
those  working  along  the  lines  mentioned  have  said  little,  for  the  reason 
that  they  have  been  attempting  to  secure  practical  results  rather  than 
popular  approval,  and  they  have  furthermore  wished  to  avoid  the  ex- 
amples others  have  set  in  rushing  into  print  without  sufficient  founda- 
tion for  their  statements.  It  seems,  however,  that  many  metallurgists 
have  refrained  from  expressing  their  opinions  because  of  the  fact  that 
the  'electro-static  theory7  has  been  presented  in  such  form  that  they 
have  had  trouble  in  understanding  just  what  the  theory  is.  For  that 
reason,  I  feel  justified  in  attempting  to  define,  so  far  as  is  possible  at 
the  present  time,  what  I  consider  to  be  the  function  of  the  electro-static 
charges  observed  in  flotation. 

If  we  take  a  large  beaker  of  water,  and  drop  into  it  some  rather 
finely  ground  galena,  say  80-mesh,  it  will  be  seen  to  entrap  considerable 
air.  To  avoid  confusion,  this  may  be  removed  by  boiling  the  water, 
and  then  allowing  it  to  cool  with  the  galena  particles  on  the  bottom. 
If  then,  we  take  a  small  thistle  tube,  and  attach  to  the  small  end  a 
rubber  bulb,  we  may  immerse  the  other  end  in  the  water,  and  by  com- 
pressing the  bulb,  make  the  surface  of  the  air  at  the  lower  end  convex. 
We  have,  then,  a  bubble  on  a  handle,  with  which  we  can  study  the  man- 
ner in  which  particles  attach  themselves  to  air-bubbles.  See  Fig.  1. 
If  we  bring  this  bubble  into  contact  with  the  galena  particles  on  the 
bottom,  and  then  slowly  withdraw  it,  the  galena  will  be  seen  to  ad- 
here to  the  surface  of  the  bubble.2  This  phenomenon,  in  my  opinion, 


*J.  M.  Callow,  Bull.  A.  I.  M.  E.,  Dec.  1915. 

iM.  &  S  P.,  Nov.  27  and  Dec.  11,  1915. 

20.  C.  Ralston,  M.  &  S.  P.,  April  29,  1916. * 


ELECTRO-STATICS 


201 


represents  flotation  in  its  simplest  form.  Many  interesting  variations 
can  be  made  in  this  experiment,  from  which  considerable  information 
can  be  obtained.  If  distilled  water  is  used,  quartz  particles  can  also 
be  made  to  adhere  to  the  bubble,  but  this  adhesion  disappears  almost 
completely  upon  the  addition  of  a  little  acid  or  other  electrolyte  to  the 
water.  A  most  important  point  to  be  observed  is  that,  from  above, 
small  points  of  the  particles  can  be  seen  protruding  through  the  bub- 


FIG.  1 


ble-film,  their  relationship  being  somewhat  as  shown  in  section  in  Fig. 
2,  the  surface-films  of  the  particle  and  the  bubble  having  become  con- 
tinuous. When,  on  the  other  hand,  quartz  is  placed  in  slightly  acid- 
ulated water,  and  the  bubble  brought  into  contact  with  it,  the  surface- 
films  do  not  coalesce  with  each  other  and  expose  the  quartz  to  the  air, 
as  occurred  with  the  galena,  but  remain  unruptured,  somewhat  as 
shown  by  Fig.  3. 

All  these  phenomena  are  manifestly  connected  with,  and  dependent 


202  FLOTATION 

upon,  the  matter  of  surface-films,  surface-tension,  and  contact-angles. 
Let  us,  therefore,  consider  the  molecular  forces  that  underlie  these 
much-discussed  properties  of  liquid  surfaces. 

In  Fig.  4,  a  molecule  of  liquid  in  the  interior  will  be  attracted  by 
the  molecules  adjacent  to  it  in  all  directions,  and  the  resultant  of  the 
cohesive  forces  acting  upon  it  will  therefore  be  zero.  (By  'molecule' 
we  do  not  refer  to  chemical  molecules,  but  to  physical  molecules — 
extremely  small  portions  of  the  liquid,  which,  however,  may  still  be 
considerably  larger  than  chemical  molecules.)  A  molecule  at  the  sur 


FIG.  2 


face,  on  the  other  hand,  will  not  be  equally  attracted  in  all  directions. 
The  attractions  in  the  plane  of  the  surface  will  balance  each  other,  but 
the  attraction  of  the  molecules  toward  the  interior  will  not  be  balanced 
by  anything.  The  resultant  of  the  forces  acting  upon  a  molecule  at 


FIG.  3 


the  surface  will  consequently  lie  in  a  line  normal  to  the  surface,  and 
toward  the  interior.  In  other  words,  a  molecule  at  the  surface  will  be 
strongly  drawn  toward  the  interior. 

Now,  if  a  molecule  of  the  liquid  responds  to  this  attraction,  and 
leaves  the  surface,  the  surface  will  naturally  tend  to  close  in  around 
the  space  left,  giving  rise  to  what  we  call  'surface-tension.'  Con- 
versely, if  we  desire  to  extend  the  surface  (as  in  blowing  a  soap-bub- 
ble larger,  or  distorting  a  drop  of  liquid),  we  must  supply  sufficient  en- 
ergy to  draw  the  requisite  molecules  from  the  interior  to  form  the  new 
surface.  Obviously,  there  are  several  means  of  measuring  this  sur- 


ELECTRO-STATICS 


203 


face-tension,  and  these  measurements  show  that  any  pure  liquid  in  con- 
tact with  a  given  gas  will  have  a  constant  surface-tension,  and  that 
the  effect  of  frothing-agents  is  to  alter  this  surface-tension  (generally 
to  lower  it),  and  to  make  it  variable. 

The  same  effects  are  observed  when  two  immiscible  liquids  come 
into  contact.  The  interfacial  tension  here  can  likewise  be  measured. 
For  these  reasons,  we  are  more  or  less  justified  in  assuming  that  the 


Fie.  4 


same  things  happen  when  a  liquid  comes  into  contact  with  a  solid.  See 
Fig.  5.  Here  a  molecule  at  the  interface  will  be  attracted  by  the  other 
molecules  of  the  liquid  in  the  same  manner  as  at  a  liquid-gas  contact, 
but  these  forces  may  be  balanced  by  the  adhesive  attraction  of  the 
molecules  of  the  solid.  There  is  evidence  to  show  that  this  attraction 
may  be  as  large  as,  or  larger  than,  the  cohesive  attraction  of  the  liquid ; 
and  if  it  more  than  balances  it,  the  resultant  of  the  molecular  forces 
acting  upon  a  molecule  at  the  interface  would  lie  toward  the  solid. 
This  would  mean  that  the  interfacial  tension,  if  there  were  any,  would 
be  negative,  and  that  the  surface  in  contact,  instead  of  tending  to  con- 
tract, would  tend  to  expand  so  as  to  wet  as  much  as  possible  of  the 
solid.  The  existence  of  interfacial  tension  in  such  cases,  either  posi- 
tive or  negative,  is  more  or  less  a  matter  of  conjecture,  but  the  forces 
which  cause  the  effect  are  known  to  exist  beyond  any  doubt;  and, 
whether  we  can  measure  them  or  not,  they  also  result  in  other  phenom- 
ena from  which  we  can,  in  some  degree,  estimate  their  relative  magni- 
tudes. From  the  standpoint  of  flotation,  the  most  important  other  phe- 


204 


FLOTATION 


nomena  are  the  cases  where  the  three  phases  meet,  a  solid,  a  liquid, 
and  a* gas.  See  Fig.  6.  Now  a  molecule  at  the  meeting-point  (the  toe 
of  the  meniscus)  will  be  acted  upon  by  several  attractions :  the  other 
molecules  of  the  liquid  will  exert  a  cohesive  attraction  upon  it,  the  re- 


5ohd 


L  i  a.  u  i  d 


FIG.  5 

sultant  of  which  will  lie  along  the  bisector  of  the  angle  between  the  gas 
and  solid  faces — the  line  C  in  Fig.  6.  The  molecules  of  the  solid  will 
exert  an  adhesive  attraction  upon  it,  the  resultant  of  which  will  lio 


Gas 


perpendicular  to  the  face  of  the  solid,  and  toward  it — the  line  A  in 
Fig.  6 — and  the  gas  may  exert  a  slight  adhesive  attraction,  probably 
negligible.  In  addition  to  these  attractions,  the  shape  of  the  meniscus 
will  also  be  affected  by  the  gas-liquid  surface-tension,  and  by  gravity. 


ELECTRO-STATICS 


205 


The  resultant  of  all  these  forces  may  lie  toward  the  liquid  or  toward 
the  solid,  but  in  either  case,  the  toe  of  the  meniscus  must  lie  perpen- 
dicular to  it  in  order  to  be  in  equilibrium.  This  resultant,  therefore, 
determines  what  we  call  the  'contact-angle'  (</>  in  Fig.  6).  Since  all 
of  the  above  mentioned  forces  should  be  constant  for  any  given 
combination  of  gas,  liquid,  and  solid,  we  should  expect  that  the  re- 
sulting contact-angle  would  be  constant  in  value  for  such  given 
combination.  Experimentally,  this  is  found  to  be  true  in  some 
cases,  but  in  other  cases  variations  are  noticed,  which  indicates  that 
other  forces,  of  a  variable  nature,  enter  into  the  matter.  Such  varia- 
tion in  value  is  called  'hysteresis',  and  in  some  cases  seems  to  be  due 
to  an  attraction  between  the  surface  of  the  solid  and  the  surface  of  the 
gas  acting  across  the  thin  film  at  the  toe  of  the  meniscus.4  Of  course, 
with  solids  whose  contact-angles  exceed  90°  (see  Fig.  7)  there  would  be 


FIG.  7 


no  thin  film  when  the  solid  surface  stood  perpendicular,  but  the  angles 
are  measured  by  turning  the  solid  until  the  liquid  apparently  'wets'  the 
solid,  and  it  will  be  seen  by  consulting  the  references  that  the  condi- 
tions under  which  the  hysteresis  is  noticed  and  measured  conform  to 
the  explanation.  It  might  easily  be  assumed  from  a  hasty  considera- 
tion of  the  above  that  all  that  is  necessary  for  a  mineral  particle  to  ad- 
here to  an  air-bubble  is  that  its  contact-angle  should  be  great,  as  in 
Fig.  7.  This  theory  is  constantly  cropping  up  in  technical  literature, 
but  it  has  a  serious  fault  in  that  it  does  not  conform  to  experimentally 
determined  facts.  The  true  parallelism  has  been  known  for  years,  and 
was  outlined  by  T.  J.  Hoover  in  his  book,  '  Concentrating  Ores  by  Flo- 
tation. '  It  is  this :  that  minerals  which  tend  to  float  are  those  in  which 
the  greatest  hysteresis  is  observed  in  the  value  of  the  contact-angle. 
Since  repeated  experiments  have  proved  this  to  be  true,  we  must  look 
for  an  explanation  of  why  this  hysteresis,  or  its  causes,  should  also  be 
connected  with  adhesion  to  air-bubbles  in  a  froth. 


4H.  Hardy  Smith,  M.  &  S.  P.,  July  1,  1916.    H.  Livingstone  Sulman,  Trans. 
I.  M.  &  M.  Bull.  79   (April  19,  1911). 


206 


FLOTATION 


When  a  mineral  particle  under  water  comes  into  contact  with  a 
bubble  of  air  (see  Fig.  8)  it  might  appear  that  the  dense  surface-films 
of  liquid  surrounding  each  would  keep  the  air  from  getting  into  ac- 
tual contact  with  the  mineral.  C.  Terry  Durell  has  gone  so  far  as  to 
say  that  this  contact  absolutely  cannot  take  place,5  but  experiments 
such  as  were  described  earlier  in  this  paper  cast  considerable  doubt  on 
the  accuracy  of  his  stand.  A  consideration  of  the  surface-tensions  in- 


FIG.  8 


volved,  however,  will  not  account  for  a  rupture  of  the  films,  since  in 
the  parallelogram  in  Fig.  8,  the  resultant  of  Tg  and  Ts  can  never 
exceed  their  sum.  Since  it  may  be  difficult  to  draw  a  clear  mental  pic- 
ture of  what  happens  when  a  solid  particle  and  a  bubble  meet,  let  us 
consider  what  happens  when  two  air-bubbles  meet.  See  Fig.  9. 

If  two  air-bubbles  submerged  in  water  impinge  against  one  another, 
a  thin  and  probably  flat  film  of  water  will  be  left  separating  them — at 
least  momentarily.  This  film  will  have  typical  surface-layers  on  either 
side.  If  the  water  is  pure,  this  film  will  not  be  stable,  since  the  surface- 
tension  will  be  constant,  and  the  upper  part  of  the  film  will  have  to 
support  not  only  the  tension  of  the  lower  part,  but  also  its  weight. 
An  equilibrium  is  therefore  impossible.  If,  on  the  other  hand,  some 
frothing-agent,  such  as  soap  or  oil,  were  present  in  the  water,  the  ten- 
sion would  not  be  constant,  but  would  be  greater  in  a  freshly  formed 


'Durell,  M.  &  S.  P.,  Sept.  18,  1915,  and  M.  &  C.  E.,  March  1,  1916. 


ELECTRO-STATICS 


207 


film  than  in  an  older  film,  and  an  equilibrium  would  therefore  be  pos- 
sible so  long  as  the  separating  film  contained  sufficient  bulk-water  from 
which  to  form  new  surface  to  take  care  of  mechanical  stresses.  From 
these  considerations,  we  would  expect  that  air-bubbles  would  unite  in 
pure  water,  while  they  -would  remain  separate  in  water  containing 
soap  or  other  frothing-agent.  This  is  exactly  what  is  observed  when  a 
large  number  of  small  bubbles  are  passed  into  water  and  into  soap  so- 
lution. It  has  at  various  times  been  pointed  out  that  a  frothing-agent 
is  introduced  into  the  pulp  in  notation  for  the  express  purpose  of  en- 
abling small  bubbles  to  exist  in  the  presence  of  each  other  and  of 
larger  bubbles  without  coalescing.  Now,  if  the  surface-film  surround- 


FIG.  9 


ing  a  sulphide  particle  is  similar  to  that  surrounding  an  air-bubble,  as 
it  very  probably  is,  we  would  expect  that  this  same  frothing-agent 
would  prevent  the  bubble-film  from  coalescing  with  the  film  surround- 
ing the  particle.  We  know,  however,  that  the  films  surrounding  par- 
ticles of  floatable  minerals,  those  which  we  previously  said  were  af- 
flicted with  "hysteresis  of  the  contact-angle,"  actually  will  coalesce 
with  the  films  of  air-bubbles.  Let  us  consider  how  this  may  be  ex- 
plained. 

It  has  been  already  mentioned  that  hysteresis  of  the  contact-angle 
might  be  due  to  some  attraction  between  the  surface  of  the  solid  and 
of  the  gas  across  the  thin  film  at  the  toe  of  the  meniscus.  If,  in  Fig.  9, 
there  were  some  attraction  between  the  surfaces  of  the  right-hand  bub- 
ble and  the  left-hand  bubble,  even  in  the  presence  of  a  frothing-agent, 
this  attraction  would  tend  to  squeeze  out  the  intervening  film,  thus  re- 
ducing the  amount  of  bulk-water  in  it,  and  its  stability  would  be 
threatened  by  the  lack  of  liquid  from  which  fresh  surface  could  be 
formed.  The  film,  in  other  words,  would  be  pinched  out.  Now,  if  the 
left-hand  bubble,  instead  of  being  a  bubble,  were  a  solid  particle,  the 


208  FLOTATION 

same  thing  would  happen,  and  it  now  begins  to  appear  logical  that 
the  same  forces  which  cause  hysteresis  of  the  contact-angle  should  also 
cause  adhesion  to  air-bubbles  in  an  oiled  pulp,  since  when  the  films 
have  once  ruptured,  the  contact-angles  of  most  floatable  minerals  will 
easily  account  for  the  particles  being  held  in  the  film.  These  same 
phenomena  have  been  observed,  and  the  same  conclusion  arrived  at, 
and  stated  in  various  forms  by  several  theorists.6  and  I  agree  with  the 
statements  of  most  of  them  concerning  this  phase  of  the  matter.  We 
can  then,  if  we  wish,  say  that  minerals  which  float  are  those  which 
have  considerable  hysteresis  in  their  contact-angles,  or  that  they  are 
not  'wetted'  by  water,  and  let  the  matter  drop,  but  in  so  doing,  we 
have  hardly  solved  the  problem.  The  reason  for  desiring  a  theory  of 
flotation  is  to  give  the  metallurgist  a  method  of  attack  for  the  prob- 
lems he  meets,  and  in  stopping  at  this  point  we  have  given  him  but 
little  help  in  the  solution  of  his  difficulties.  Unless  we  can  determine 
some  of  the  controlling  causes  of  this  hysteresis,  unless  we  can  hope  to 
learn  how  to  introduce  or  remove  it  to  suit  our  needs,  our  time  has 
been  largely  wasted. 

I  have  done  a  great  deal  of  experimental  work  during  the  past  year 
and  a  half,  most  of  which  consisted  of  a  study  of  the  possible  causes 
of  hysteresis  of  the  contact-angles.  The  net  result  of  this  work  has 
been  to  show  that  there  are  several  possible  causes,  only  one  of  which 
has  seemed  to  be  noticeably  selective  in  its  action.  This  one  is  the  pres- 
ence of  electro-static  charges  of  different  polarities  on  the  surfaces  of 
the  floatable  particles  and  of  the  bubbles.  To  return  to  Fig.  9,  if  we 
imagine  the  surface  of  the  left-hand  bubble  to  be  covered  with  a  posi- 
tive charge,  and  the  surface  of  the  right-hand  bubble  to  be  similarly 
covered  with  a  negative  charge,  it  is  clear  that  these  charges  would 
give  rise  to  an  attraction  across  the  intervening  film  of  the  sort  previ- 
ously described  as  being  necessary  to  cause  the  film  to  rupture.  If, 
however,  both  bubbles  were  covered  with  charges  of  the  same  polarity, 
the  two  sides  of  the  film  would  repel  one  another,  which  would  tend 
to  increase  the  thickness,  and  consequently  the  stability  of  the  film. 
Again,  the  same  results  would  occur  were  the  left-hand  bubble  occu- 
pied by  a  particle  of  mineral.  It  has  been  repeatedly  observed  in  the 
course  of  my  experiments  that  the  conditions  best  suited  for  flota- 
tion were  those  under  which  the  valuable  minerals  bore  the  highest 
positive  charges  and  the  gangue-minerals  and  bubbles  considerable 
negative  charges.  These  charges  must  not  be  confused  with  ordinary 


Hardy  Smith  and  Durell,  previously  quoted. 


ELECTRO-STATICS  209 

frictional  electricity,  which  must  be  insulated  to  be  preserved.  They 
are  due  to  the  greater  adsorption  by  the  surface  in  question  of  some 
kinds  of  ions  than  of  others,  resulting  in  a  concentration  of  ions  of  one 
polarity  or  the  other  against  the  surface.7  To  the  extent  of  my  knowl- 
edge, there  is  no  other  cause  of  hysteresis  which  will  result  in  selective 
flotation,  all  others  seeming  to  affect  gangue  and  sulphide  minerals  to 
much  the  same  degree.  Methods  have  been  discovered  by  means  of 
which  these  charges  can  be,  to  some  extent,  controlled.  For  instance, 
when  tannine  or  saponine  is  added  to  a  properly  operating  flotation- 
cell,  the  positive  charges  on  the  sulphide  minerals  will  drop,  even  to 
the  extent  of  becoming  negative,  and  the  froth,  if  it  carries  anything 
at  all,  will  drop  in  grade  as  the  potential  drops.  It  has  also  been 
possible  to  secure  the  reverse  of  these  conditions,  the  grade  of  the 
froth  being  made  to  rise  as  the  proper  electrical  conditions  are  created. 
In  doing  this,  it  is,  of  course,  necessary  to  minimize  the  effects  of  all 
other  possible  causes  of  hysteresis. 

In  regard  to  the  effect  of  tannine,  saponine,  and  similar  colloids,  it 
has  been  suggested  once  or  twice8  that  the  disastrous  results  following 
the  addition  of  these  substances  was  due  to  their  effect  on  the  condi- 
tion of  the  oil.  This  is  by  no  means  impossible,  but  I  wish  to  state  most 
distinctly  that  I  have  never  seen  these  disastrous  results  occur  when  an 
electro-positive  colloid  was  added,  nor  have  I  ever  tried  an  electro- 
negative colloid  that  did  not  kill  the  flotation.  Since  the  science  of 
colloidal  chemistry  is  practically  based  upon  these  electro-static 
charges,  this  may  mean  any  of  several  things,  but  no  explanation  of 
the  effects  of  colloids  on  flotation  should  overlook  these  facts. 

The  reader  must  be  cautioned  against  assuming  from  the  above 
that  a  detailed  explantion  of  flotation  can  yet  be  given.  Colloidal 
chemists  have  yet  to  agree  upon  the  explanation  of  many  of  the 
phenomena  to  be  observed  in  connection  with  surficial  and  interfacial 
films,  and  the  experimental  possibilities  of  the  work  have  only  been 
scratched.  I  believe,  however,  that  work  done  so  far  permits  of  the 
following  conclusions: 

1.  The  tendency  displayed  by  particles  of  certain  minerals  to  at- 
tach themselves,  under  proper  conditions,  to  air-bubbles  in  an  oiled 
pulp  is  due  to  the  presence  of  considerable  hysteresis  in  the  value  of 
their  contact-angles  with  air. 


7Powis,  Trans.  Faraday  Society,  April  1916,  p.  160. 

«Van  Arsdale,  Bull.  A.  I.  M.  B.,  May  1916,  p.  885;  Bancroft,  Met.  &  Chem. 
Eng.,  June  1,  1916. 


210 


FLOTATION 


2.  This  hysteresis  may  result  from  any  of  several  causes,  some  of 
which  are  fairly  well  understood,  and  some  of  which  are  still  some- 
what puzzling. 

3.  A  great  many  of  these  causes  do  not  seem  to  be  selective  in  their 
action,  but  result  in  the  flotation  of  both  gangue  and  metallic  minerals. 

4.  The  cause  which  seems  to  result  in  the  selective  flotation  of  sul- 
phide minerals  is  the  possession  by  these  minerals  of  positively  charged 
contact-films  of  liquid  surrounding  them,  while  the  gangue  and  air- 
bubbles  possess  negatively  charged  films. 

I  wish  to  express  my  thanks  to  J.  M.  Callow,  at  whose  instigation 
this  work  was  taken  up,  for  his  kindness  in  permitting  these  results 
to  be  published,  and  for  his  help  and  advice  in  the  interpretation  of  the 
results.  I  also  wish  to  express  my  appreciation  of  the  assistance  ren- 
dered by  O.  C.  Ralston  in  the  collecting  of  scientific  data  concerning 
flotation. 


FROTH    WITH    0.1%    OIL,    MAGNIFIED    400    TIMES 


THEORY    OF    ORE    FLOTATION  211 


THEORY  OF  ORE  FLOTATION 

By  H.  P.  CORLISS  and  C.  L.  PERKINS 
(From  the  Mining  and  Scientific  Press  of  June  9,  1917) 

*The  physics  and  chemistry  of  ore  notation  constitute  the  subject 
of  extensive  literature,  but  no  one  contribution  presents  an  explana- 
tion of  all  the  physico-chemical  factors  involved.  These  articles1  in- 
clude collectively  considerable  information  of  importance,  but  have 
failed  to  elucidate  this  very  obscure  problem. 

In  this  paper  is  presented  an  explanation  of  the  actual  factors 
involved  in  ideal  flotation  and  also  of  other  practical  observations 
incident  to  the  art.  The  theory  presented  herein  has  been  substan- 
tiated by  actual  experiment,  but  only  a  brief  resume  of  the  experi- 
mental results  is  included. 

The  greatest  success  in  the  art  has  been  obtained  in  processes  in 
which  a  gas,  usually  air,  is  introduced  into  the  pulp,  either  by  chemical 
means  from  carbonate  and  acid  (Potter-Delprat  process),  assisted  by 
vacuum  (Elmore  process),  by  the  use  of  agitation  (Minerals  Sep- 
aration process),  or  by  blowing  it  in  through  a  porous  blanket 
(Callow  process),  and  with  or  without  the  use  of  oil.  The  explana- 
tion offered  in  this  paper  is  for  this  type  of  process  especially, 
although  the  simple  flotation-principles  involved  in  such  processes  as 
the  Macquisten,  the  Wood,  and  the  bulk-oil  process,  are  included.  In 
all  these  processes  the  material  floated  must  not  be  wholly  wet  by  the 
water  or  solution  in  the  presence  of  this  gas  or  the  material  surround- 
ing this  gas,  for  example,  an  oil-film  on  the  bubble-surface.  If  the 
material  is  completely  wet  by  the  water,  it  will  not  float,  which  is  the 
case  of  the  ideal  gangue,  while  the  material  floated  must  'go  to  the 
interface  water-air  bubble  or  entirely  into  the  phase  other  than  water, 
that  is,  the  oil  on  the  air-bubble. 

The  relations  of  the  forces  acting  to  produce  this  result  were  first 


*Jour.  Ind.  &  Eng.  Chem.,  May  1917. 

iSee  especially  the   following:     W.   D.   Bancroft,  Jour.  Phys.   Chem.,   19 
(1915),  275;  Ralston,  M.  &  S.  P.,  Oct.  23,  1915;  Callow,  Bull.  A.  I.  M.  E.,  Dec. 

1915,  2321;   Anderson,  Ibid.,  July  1916,  1119;   and  Taggert  and  Beach,  IMd., 
Aug.  1916,  1373.     For  a  very  complete  bibliography,  see  School  of  Mines  & 
Metallurgy,  Univ.  of  Missouri,  Bull.  8,  No.  1,  1916;    also  Bull.  A.  I.  M.  E., 

1916,  1131. 


212  FLOTATION 

stated  by  Freundlich2,  and  enlarged  upon  by  Hoffman3  and  Reinders.4 

They  were  first  stated  for  the  behavior  of  a  sol,  which  will  be  called 

disperse  phase  3  in  liquid  1,  when  shaken  with  an  immiscible  liquid 

2.    Let 

T±  3  =  interfacial  tension  between  phase  3  and  liquid  1. 

T2  3  =  interfacial  tension  between  phase  3  and  liquid  2. 

TI  2  =  interfacial  tension  between  the  two  liquids. 

If  T2  3  >  Z\  3  +  TI  2  the  sol  will  remain  unchanged ; 

If  2\  3  >  T2  3  -f-  ^i  2  the   disperse  phase  3   will   go   entirely  into 

liquid  2 ; 

If  T1  2  >  T2  3  +  Tj_  3  the  disperse  phase  will  collect  at  the  liquid- 
liquid  interface  and  will,  if  possible,  separate  the  two  liquids 
from  each  other. 

If,  however,  no  one  interfacial  tension  is  greater  than  the  sum  of 
the  other  two,  then  the  disperse  phase  will  collect  at  the  liquid-liquid 
interface,  but  the  three  phases  will  meet  at  a  certain  contact-angle. 
The  application  of  these  principles  to  flotation  may  now  be  stated,  for 
while  the  greater  part  of  the  material  floated  is  much  less  disperse  than 
that  which  is  considered  colloidal,  the  interfacial  tendencies  are  the 
same,  it  simply  being  a  question  whether  the  forces  holding  the  min- 
eral to  the  interface  are  sufficient  to  overcome  gravity,  if  the  particle 
is  to  float. 

Methods  of  flotation  without  resort  to  the  use  of  oil  are  exemplified 
in  the  well-known  Potter-Delprat  process,  in  which  C02  is  generated 
in  the  acid  pulp,  but  may  be  carried  out  successfully  on  some  ores  in 
a  Callow  cell,  using  air.  Here,  if  flotation  is  to  result,  the  mineral  must 
go  to  the  interface  water-gas  and  be  carried  at  this  interface  to  the  top 
of  the  pulp.  The  word  water  will  be  used  mostly  to  denote  the  aque- 
ous phase,  whether  it  is  pure  water  or  a  solution,  and  the  floatable 
material  will  be  called  sulphide,  since  this  is  the  common  case.  On  the 
basis  of  interfacial  tensions,  where  if 

T8    a  ==  interfacial  tension  sulphide-air  (or  CO,), 

TH  w  =  interfacial  tension  sulphide-water, 

Tw  a  =  surface-tension  water-air  (or  CO.,), 

either  (1)  T*  w  >  Ts  „  -f-  Tw  a  or  (2)  no  one  interfacial  tension  is 
greater  than  the  sum s  of  the  other  two,  must  be  true.  It  is  obviously 
impossible  to  have  Tw  a  >  Ts  a  -f  Ts  w  as  the  latter  two  are  very  large 
in  comparison  with  the  first,  according  to  theoretical  reasoning  and 


2'Kapillarchemie,'  1909,  137,  174. 
zZeit.  phys.  Ghem.,  83  (1913),  384. 
^Kolloid  Zeit.,  13  (1913),  235. 


THEORY    OF"  ORE    FLOTATION  213 

measurements.5  Case  2  is  the  actual  one,  as  can  be  seen  if  a  drop  of 
water  is  placed  on  a  flat  sulphide  surface.  Here  the  water  does  not 
spread  over  the  entire  surface,  but  comes  to  equilibrium  with  the 
three  phases,  sulphide,  air,  and  water  in  contact  at  a  certain  angle. 
Case  1  would  require  that  the  water  should  not  wet  the  sulphide  at  all 
in  the  presence  of  air.  In  flotation  then  the  sulphide  comes  to  the 
air-water  interface  and  sticks  through  the  bubble-surface  to  a  certain 
extent,  or  is  held  in  such  a  way  that  the  three  phases  are  in  contact. 
The  gangue  material  is  completely  wet  by  water  and  does  not  float, 
that  is,  Tg  a  >  Tg  w  +  Tw  a. 

Some  measurements  were  made  to  get  an  idea  of  these  interfacial 
tendencies,  by  a  method  explained  in  connection  with  Fig.  1.  Here  a 
flat-ground  mineral-surface  was  placed  vertically  in  water  or  other  so- 
lution as  shown.  By  raising  and  lowering  the  mineral,  a  quite  constant 
result  was  obtained  for  the  rise  of  the  meniscus  against  the  mineral 
above  the  general  level.  Here  the  meniscus  was  always  upward,  show- 
ing a  greater  preference  of  the  mineral  for  water  than  for  air.  In  the 
case  of  the  sulphides,  when  they  were  raised,  the  meniscus  would  soon 
draw  back  to  a  definite  height,  leaving  the  sulphide  surface  above  quite 
dry.  For  gangue  the  water  does  not  draw  back  quickly,  but  remains, 
wetting  it  for  some  time.  The  sulphides  are  proved  interfacial  in  this 
way,  and  the  measurements  of  the  height  of  the  point  of  contact  above 
the  general  level  are  interesting.  The  measurements  were  made  with  a 
cathetometer. 

Water,  0.1%  H2SO4         0.1%  NaOH, 

Material  •  mm.  mm.  mm. 

Chalcocite     1.55  2.10  3.07 

Chalcopyrite 2.60  2.50  2.90 

Gangue    (silicate)    3.20  3.25  3.30 

The  figures  for  the  gangue  are  not  at  the  point  of  contact,  for  there 
is  none,  since  it  is  thoroughly  wet  by  water,  but  are  at  the  point  where 
the  meniscus  becomes  parallel  to  the  face  of  the  mineral  surface.  The 
mineral  giving  the  smallest  rise  should  be  the  most  interfacial  and  the 
best  floating.  This  was  found  to  be  true,  for,  without  oil,  chalcocite 
is  a  better  floating  mineral  than  chalcopyrite,  at  least  for  the  ores  that 
were  tested.  The  figures  above  also  show  that  in  alkaline  solution  a 
very  poor  float  should  be  made,  as  the  rise  is  almost  as  much  as  for  the 
gangue.  This  was  also  found  to  be  true.  Differences  even  among 
sulphides  are  clearly  shown,  hence  it  is  not  surprising  to  find  all  grada- 
tions in  floating  properties  among  ores.  These  measurements,  made 


sHulett,  Zeit.  phys.  Chem.,  37    (1901),  385.     Also  the  surface-tensions  of 
molten  metals  and  fused  salts  are  high. 


214  FLOTATION 

on  large  pieces  of  mineral,  with  ground  and  partly  polished  surfaces, 
may  not  correspond  exactly  to  those  for  an  ore-surface,  though  in  the 
cases  mentioned  they  were  found  to  give  results  agreeing  with  practice. 
Another  point  noticed  in  these  measurements,  which  is  an  impor- 
tant one,  is  how  quickly  the  water  is  displaced  from  a  mineral-surface 
when  brought  in  contact  with  air.  If  an  air-bubble  comes  in  contact 
with  a  sulphide  particle  immersed  in  water,  it  must  partly  displace 
the  water  from  the  sulphide  rather  quickly  if  it  is  to  be  floated  in  a 
pneumatic  cell.  This  was  tested  for  the  same  minerals,  by  noting  the 
time  taken  for  the  solution  to  come  back  to  the  final  point  of  contact, 
when  the  mineral  was  raised,  with  the  following  general  results : 

(1)  Water  and  acid  solutions  are  removed  more  quickly  in  air 
from  chalcocite  than  from  chalcopyrite. 

(2)  Little  difference  is  noted  between  acid  and  neutral  solutions. 

(3)  Alkaline  solutions  are  removed  very  slowly  from  all  sources. 

(4)  All  solutions  adhere  strongly  to  gangue. 

These  facts  also  agree  with  the  practical  results  mentioned  above. 
The  success  of  the  Potter-Delprat  process  may  well  be  due  to  these 
facts,  since  the  CO2  is  generated  in  contact  with  the  sulphide,  and  time 
is  given  for  the  solution  to  be  partly  displaced  by  the  gas  or,  in  other 
words,  for  the  sulphide  to  attain  the  interfacial  condition  and  be 
floated.  When  a  soluble  frothing  agent  is  used,  without  oil,  the  same 
principles  apply,  the  frothing  agent  simply  modifying  the  water  to  a 
certain  extent. 

The  use  of  oil  introduces  several  new  factors  which  make  the  prob- 
lem more  complex,  but  the  same  principles  apply. "  The  sulphides  can 
now  be  interfacial  between  water  and  air  as  discussed  above,  but,  in 
addition,  may  be  interfacial  between  water  and  oil,  or  even  go  into 
the  oil-layer.  This  oil-layer  is  on  the  bubble-surface  and  the  forces 
holding  the  sulphides  to  this  surface,  if  it  has  an  oil-film,  are  much 
greater  than  when  no  oil  is  used.  This  point  will  be  proved  a  little 
further  on.  The  oil-layer  on  the  bubble-surface  need  be  only  of  mini- 
mum thickness  to  act,  in  contact  with  water,  the  same  as  a  layer  of  oil 
on  water,  as  far  as  interfacial  tendencies  are  concerned.  Let 

T*  w  =  interfacial  tension  sulphide-water, 

Ts    o  =  interfacial  tension  sulphide-oil, 

T0  w  =  interfacial  tension  oil-water. 

Then,  if  (1)  T,  w  >  Ts  0  +  T0  w,  the  sulphide  will  go  into  the 
oil-layer  completely;  (2)  no  one  interfacial  tension  is  greater  than  the 
sum  of  the  other  two,  the  sulphide  will  go  to  the  oil-water  interface, 
and  the  three  phases  will  be  in  contact  at  a  certain  contact-angle.  The 


THEORY    OF    ORE    FLOTATION 


215 


gangue  is  thoroughly  wetted  by  water,  that  is,  Tg  0  >  Tg  w  +  T0  w. 
These  inequalities  have  been  stated  and  applied  to  the  flotation 
process  by  Ralston.0.  The  second  condition  given  above,  where  the 
sulphides  are  interfacial,  seems  to  be  by  far  the  most  general,  though 
the  first  condition  may  be,  and  probably  is,  realized,  especially  when 
tarry  oils  are  used,  which,  in  grinding  with  the  ore,  coat  the  sulphides 
more  or  less  with  this  tarry  material.  It  is  doubtful  if  the  lighter  oils 
or  the  lighter  constituents  of  a  tarry-oil  mixture  film  the  sulphide  at 
all  in  grinding,  but  rather  it  is  probable  that  this  oil  is  emulsified  in 
the  operation.  The  condition  where  the  mineral  is  completely  filmed 
by  oil  would  be  the  best  floating  condition,  and  this  could  be  realized 


Air 


Wafer 


F/gJ. 


in  the  flotation  cell,  where  this  film  would  be  continuous  with  the  oil- 
film  on  the  bubble-surface.  All  gradations  of  the  interfacial  conditions 
are  possible,  from  those  that  show  only  a  slight  tendency  to  be  wet  by 
water  in  the  presence  of  oil,  to  those  that  are  thoroughly  wet,  which 
is  the  case  of  the  gangue-material. 

Experimental  determinations  of  the  interfacial  tendencies  of  vari- 
ous minerals  were  carried  out  in  the  same  way  as  described  above, 
except  that  in  this  case  the  interface  was  oil-water,  or  aqueous  solu- 
tion. In  Fig.  2  is  represented  the  case  of  a  sulphide  surface  at  this 
interface.  The  floatable  materials  were  all  interfacial,  and  the  sul- 
phides showed  a  decided  preference  for  the  oil.  This  is  an  important 
point  in  showing  that  the  same  sulphides  are  much  more  strongly  held 
to  an  oil-covered  air-bubble  than  to  one  not  so  covered.  In  Fig.  1  the 
sulphide,  while  interfacial,  shows  a  preference  for  water  over  air,  and 
would  easily  be  displaced  in  actual  flotation  from  the  interface  and  go 


«M.  &  S.  P.,  Oct.  23,  1915. 


216  FLOTATION 

back  into  the  water.  In  Fig.  2  the  meniscus  is  now  pushed  downward 
into  the  water,  instead  of  upward,  hence  the  sulphide  is  held  much 
more  strongly  to  oil  than  to  air. 

The  following  measurements  were  made  after  the  meniscus  had 
come  to  the  true  point  of  contact  of  the  three  phases,  and  this  point 
was  closely  the  same,  whether  the  mineral  was  first  wet  with  the  oil 
or  solution.  The  averages  of  these  two  figures  are  given.  Kerosene 
and  a  kerosene  pine-oil  mixture  were  used  mostly,  as  the  interfaces 
are  better  defined,  especially  in  acid  and  alkaline  solution,  than  with 
many  actual  flotation  oils.  These  other  oils  act  in  the  same  way, 
however. 

DEPRESSION  OF  MENISCUS:   KEROSENE  AND  CHALCOPYRITE 

Water  0.1%  H,SO4  1%  H,SO4  10%  H,S04 

2.99  mm.  2.02  mm.  1.32  mm.  0.75  mm. 

Calcite  in  contact  with  neutral,  acid,  and  alkaline  solutions  and 
kerosene  showed  interfacial  tendencies  in  alkaline  solution  only.  Mal- 
achite exhibited  a  small  interfacial  tendency,  except  in  alkaline  solu- 
tion in  which  it  was  thoroughly  wet  by  the  solution. 

KEROSENE  AND  PINE-OIL  AND  AQUEOUS  SOLUTION 

This  was  a  flotation  mixture  of  90%  kerosene  and  10%  pine-oil. 

Depression  of  meniscus 

Chalcopyrite,         Chalcocite, 

mm.  mm. 

Water    3.10  3.42 

0.1%  NaOH  1.98  2.54 

0.1%  H2S04    1.45  2.95 

Gangue-material  in  all  cases  is  thoroughly  wet  by  the  solution, 
especially  if  it  is  wet  by  the  solution  before  coming  in  contact  with  the 
oil,  as  is  the  case  in  actual  flotation.  The  case  of  chalcocite  in  water, 
given  above,  is  almost  a  condition  of  complete  wetting  by  oil.  These 
experimental  results  in  every  way  justify  the  theoretical  discussion 
given,  and  also  show  that  alkali  and  acid  lower  the  interfacial  tension 
sulphide-water  as  the  preference  for  oil  is  not  as  great  in  these  solu- 
tions as  in  water,  although  the  sulphide  is  still  distinctly  interfacial 
and  hence  can  be  easily  floated  from  acid  or  alkaline  pulps.  These 
results  were  obtained  by  the  use  of  a  clean  sulphide-surface,  but  in 
actual  flotation  this  may  not  be  true  for  all  the  particles,  and  since  the 
interfacial  properties  are  a  function  of  the  surface  only,  one  may  ex- 
pect many  differences  from  these  ideal  measurements.  In  alkaline 
solution,  for  example,  there  may  be  some  of  the  mineral  which,  like 


THEORY    OF    ORE    FLOTATION  217 

calcite,  is  more  interfacial  in  this  solution  than  in  water,  and  hence 
would  float,  although  it  would  not  do  so  in  a  neutral  pulp.  In  tests  it 
has  been  found  with  some  ores  and  oil-mixtures  that  in  an  alkaline  pulp 
a  better  recovery  was  made  in  the  usual  length  of  time  than  by  pro- 
longed flotation  in  neutral  pulp.  This  might  be  true  also  in  an  acid 
pulp  for  some  minerals. 

It  has  been  noticed  that  some  surfaces  have  a  strong  tendency  to 
hold  fast  to  the  liquid  first  wetting  them  and  not  to  allow  it  to  be 
easily  displaced  by  another  liquid.  In  the  work  upon  interfacial  ten- 
sion, described  above,  such  a  surface  would  show  a  great  difference 
in  preferential  action  or  angle  of  contact,  dependent  upon  whether  it 
was  wet  with  oil  or  water  first.  It  has  also  been  observed  that  it  is 
principally  those  substances  having  smooth  or  shiny  surfaces  which 
float,  while  those  having  dull  or  rough  surfaces  do  not  float.  These 
observations  and  others  point  to  the  following  explanation  of  the 
mechanism  of  this  action :  there  is  first  the  inherent  property  of  each 
substance  to  adhere  to  oil  or  to  water  to  a  certain  degree.  When  the 
substance  is  brought  to  the  interface  between  water  and  oil,  these  forces 
tend  to  come  to  equilibrium  with  the  third  force,  the  interfacial  ten- 
sion between  oil  and  water,  at  some  definite  contact-angle.  Here  is 
where  the  physical  nature  of  the  solid  surface  comes  into  play.  If  the 
surface  is  smooth  and  shiny,  such  as  that  of  a  polished  metal  or  a 
freshly  fractured  sulphide  crystal,  then  the  liquid  first  touching  it  is 
easily  pushed  back  to  the  position  of  equilibrium.  If,  however,  the 
substance  has  a  dull,  that  is,  a  capillary  surface,  so  that  the  liquid  first 
wetting  it  is  strongly  held  in  its  pores,  then,  when  it  is  brought  to  the 
interface  it  may  exhibit  no  interfacial  properties  at  all,  although,  if  it 
were  smooth,  it  might  even  show  a  preference  for  the  other  liquid. 
This  shows  the  reason  for  the  difference,  or  hysteresis,  of  the  contact- 
angle  noted  for  some  surfaces.  It  also  explains  why  a  particle  having 
such  a  surface,  if  first  wet  with  water,  as  is  the  case  in  flotation,  will 
be  very  difficult  to  float,  since  it  will  not  easily  be  brought  into  contact 
with  oil. 

The  function  of  the  bubble  is  to  give  a  large  surface  to  which  the 
sulphide  may  go  and  be  floated.  As  already  stated,  the  air-bubble  in 
oil-flotation  is  covered  wholly  or  in  part  by  an  oil-film.  For  the  action 
of  oil  on  water,  see  Devaux7  and  Langmuir-8  It  is  not  necessary  that 
the  oil  completely  cover  the  bubble,  and  it  probably  does  not  in  the 
greater  proportion  of  the  bubbles.  The  supply  of  oil  for  the  bubbles  will 


•  Ann.  Report  Smithsonian  Inst.,  1913,  261. 
*Met.  cC-  Chem.  Enff.,  15  (1916),  469. 


218  FLOTATION 

be  discussed  under  the  action  of  emulsions.  If  an  oil  droplet  be  placed 
on  water  or  aqueous  solution,  it  will  spread  over  the  surface  provided 
the  surface-tension  of  the  water  is  greater  than  the  sum  of  the  surface- 
tension  of  the  oil  plus  the  interfacial  tension  oil-water,  that  is,  this 
inequality  must  be  true : 

T          ^   T        -U  T 

-*-  w    a   ^    -*-  o    a     |      -*•  o    w 

For  oil-flotation  this  must  be  true  for  all  solutions  used,  as  the  air  in 
the  bubble,  surrounded  by  the  pulp,  presents  this  same  condition.  If  to 
water  be  added  some  material  which  lowers  its  surface-tension  (Tw  «.), 
without  lowering  Tw  a  -\-  T0  a  to  an  equal  amount,  the  inequality  is 
reduced,  and  finally  a  point  is  reached  where  the  oil  will  not  spread  on 
the  solution.  This  is  easily  realized  in  the  case  of  soap-solutions,  and 
with  many  other  substances  that  lower  the  surface-tension  greatly.  In 
this  condition  a  poor  float  would  result.  In  flotation,  in  order  to  pro- 
duce a  froth,  material  such  as  the  soluble  portion  of  pine-oil  is  added 
which  lowers  the  surface-tension  of  water.  Unless  this  helps  in  other 
ways  than  in  producing  a  froth,  it  should  be  used  in  as  small  a  quan- 
tity as  possible,  and  this  agrees  with  many  practical  observations.  The 
frothing  agent  added  also  lowers  the  interfacial  tension  oil-water,  but 
here  it  must  be  remembered  that  even  if  the  interfacial  tension  be  low- 
ered in  the  same  proportion  as  the  surface-tension,  the  inequality  is  less 
than  before,  since  the  interfacial  tension  is  much  smaller  than  the  sur- 
face-tension of  water.  The  other  factor,  the  surface-tension  of  oil 
(T0  a),  is  not  changed  much,  for  inorganic  salts  do  not  dissolve  in  it. 
If,  however,  some  substance  be  added  which  will  not  lower  the  surface- 
tension  of  water  but  will  lower  the  interfacial  tension  oil-water,  then 
this  should  produce  better  oiling  of  the  bubble.  This  can  be  done  with 
alkalies  and  in  the  case  of  some  oils  by  acids. 

An  important  point  in  connection  with  the  use  of  the  pneumatic  cell 
is  the  time  during  which  the  bubble  is  in  contact  with  the  pulp  as  it 
passes  through,  as  here  it  must  be  attached  to  the  sulphide  particles. 
Any  reagent  that  will  give  a  quicker  filming  of  the  bubble-surface  by 
oil,  after  it  comes  through  the  blanket,  will  be  of  benefit  in  the  rapidity 
with  which  the  mineral  is  attached  and  raised.  Alkalies,  as  explained, 
produce  a  greater  inequality  between  Tw  a  and  Tw  0  -j-  T0  0,  and 
hence  the  oil  will  be  spread  out  quicker  over  the  surface  than  without 
their  use.  A  large  number  of  surface  and  interfacial  tension  measure- 
ments were  made,  a  few  of  which  are  as  follows : 

SURFACE  TENSION 

Dynes  per  cm. 

Water   25°  C 71.8 

Kerosene    25.2 


THEORY    OF    ORE    FLOTATION  219 

Dynes  per  cm. 

Coke-oven  oil 28.0 

Pine-oil    30.0 

0.1%  solution  terpineol    68.6 

0.1%  solution  terpenol  49.2 

INTERFACIAL  TENSIONS 

Kerosene-water     32.8 

Kerosene  and  pine  oil-water  11.6 

Kerosene  and  pine  oil-0.05%  solution  NaOH 7.3 

Kerosene  and  pine  oil-0.2%  solution  NaOH 4.5 

Kerosene  and  pine  oil-0.2%  solution  H,SOt  13.2 

Coke-oven  oil-water  14.1 

Coke-oven  oil-0.05%  solution  NaOH    5.8 

Coke-oven  oil-0.2%  solution  NaOH  2.6 

Coke-oven  oil-0.1%  solution  Na.,CO,  6.6 

Coke-oven  oil-0.2%  solution  Na^CO,   4.4 

Coke-oven  oil-0.2%  solution  Na,B,O7-10  Aq 8.0 

Coke-oven  oil-0.1%  solution  Na4P,O7-10  Aq 9.6 

Coke-oven  oil-0.2  solution  Na4P.,O7.10  Aq 7.4 

Coke-oven  oil-0.4%  solution  H.SO, 14.4 

Coke-oven  oil-0.01%  solution  saponine   9.3 

Coke  oven  oil-0.01  solution  tannic  acid 12.7 

Coke-oven  oil-0.01%  solution  hemoglobin  8.9 

Numerous  data  of  this  kind  are  given  by  Lewis9  and  Shorter  and 
Ellingsworth10  on  the  action  of  dyes,  salts,  and  soap.  The  drop-num- 
ber apparatus  used  was  the  same  as  described  by  Shorter  and  Ellings- 
worth. Their  work  also  shows  that  soap  and  alkali  together  are  ex- 
tremely active  in  lowering  the  interfacial  tension  oil-water.  This 
would  be  the  condition  in  an  alkaline  pulp,  as  there  would  then  be  free 
alkali  and  some  saponified  material  with  many  of  the  oils  used. 

The  results  when  colloidal  material  is  present  are  subject  to  great 
variation,  due  to  different  speeds  of  formation  of  drops.  The  figures 
given  above  for  these  materials  approach  the  dynamic  value,  as  the  rate 
of  Hrrnpiro1  was  fairly  rapid.  The  static  values  are  much  smaller,  and 
are  interesting  in  connection  with  the  emulsifying  power  of  these  sub- 
stances. As  an  example  of  this  the  following  result  on  coke-oven  oil 
against  0.005%  hemoglobin  solution  is  given.  The  time  is  for  the  total 
number  of  drops  formed. 

Interfacial  tension, 
Time  Drop  No.  dynes  per  cm. 

2  min.  40  sec 22.5  13.2 

I  hr.  4  min 84.0  3.5 

It  is  seen  from  the  table  above,  that  besides  NaOH  itself,  any  salt 
that  hydrolyzes  to  give  an  alkaline  solution  lowers  the  interfacial  ten- 
sion, and  all  these  salts  are  beneficial  to  flotation. 

The  behavior  of  the  oil  at  the  bubble  and  sulphide  surfaces  has  been 


»Zeit.  phys.  Chem..  74  (1910),  619. 
ioproc.  Roy.  Soc.,  92  (1916),  231. 


220  FLOTATION 

given.  In  the  pneumatic  cell  this  oil  is  supplied  by  an  emulsion  or  a 
coarser  suspension  of  oil  in  water..  In  the  agitator-type  machine,  the 
oil  may  be  beaten  in  at  the  cell,  though  it  is  also  customary  to  grind 
the  oil  with  the  ore.  In  either  case  the  problem  of  emulsions  comes  in. 
In  the  pneumatic  process  this  emulsion  is  formed  in  the  grinding  and 
must  be  good  enough  to  last  throughout  the  float,  yet  not  so  good  as  to 
fail  to  break  down  with  sufficient  rapidity  to  give  free  oil  for  the 
bubble-surface.  The  subdivision  of  the  oil  is  such  that  no  doubt  almost 
all  degrees  of  dispersion  exist ;  the  larger  droplets  may  be  of  sufficient 
size  for  one  to  coat  a  fair  area  of  a  bubble-surface,  but  the  better  emul- 
sified proportion  is  of  such  size  that  many  particles  have  to  unite  to 
give  oil  enough  for  the  minimum  thickness  of  an  oil-film,  to  spread 
over  even  a  square  centimetre.  This  can  be  calculated  from  the  min- 
imum thickness  of  .an  oil-film11  and  the  size  of  the  particles  in  an 
ordinary  oil-emulsion.12 

Experimental  evidence  on  these  points  is  conclusive.  If  a  coarse 
suspension  of  oil  be  made  simply  by  shaking  the  ore,  oil,  and  water 
together  in  a  bottle  by  hand,  and  then  put  in  a  small  Callow  cell,  only 
a  partial  float  results,  and  the  operation  must  be  repeated  several 
times,  adding  more  oil  each  time,  in  order  to  get  a  good  recovery.  If, 
however,  too  good  an  emulsion  is  had,  a  poor  recovery  results.  For 
this  purpose  a  kerosene  pine-oil  mixture  was  emulsified  with  water  in 
a  De  Laval  emulser  and  allowed  to  stand  over  night,  and  a  middle 
portion  of  this  emulsion  was  removed  for  the  tests.  This  emulsion 
added  at  the  cell  gave  a  small  float  at  first  and  then  stopped.  On  add- 
ing a  little  acid  no  further  float  resulted,  but,  by  allowing  the  pulp  to 
stand  for  a  few  minutes,  an  additional  amount  of  sulphide  was  raised, 
and  finally  a  good  recovery  was  made,  though  considerable  time  had 
to  be  given  for  the  emulsion  to  give  up  its  oil.  This  was  also  found  to 
be  true  for  another  oil  that  gave  an  excellent  emulsion  on  simply  add- 
ing it  to  water. 

It  is  interesting  to  note  that  in  these  cases  it  was  proved  that  it  was 
not  necessary  to  grind  the  oil  with  the  ore,  but,  by  adding  it  as  an  emul- 
sion prepared  by  itself,  as  good  a  recovery  results.  This  probably  is 
not  true  for  oils  containing  tarry  matter  as  explained  above.  It  was 
also  noticed  in  using  the  second  emulsion,  named  above,  that  floccula- 
tion  of  the  slime  took  place  in  neutral  solution,  and  that  these  then 
floated  to  a  large  extent,  giving  a  non-preferential  float ;  when,  on  the 
other  hand,  the  emulsion  was  broken  by  acid  and  alum,  a  good  prefer- 


uDevaux,  LOG.  cit. 

Zeit.  phys,  Chem.,  80  (1912),  597, 


THEORY    OF    OEE    FLOTATION  221 

ential  float  resulted.  It  was  found  that  this  slime  in  neutral  pulp  had 
flocculated  with  the  oil-emulsion  so  that,  on  standing,  all  the  oil  was 
carried  down,  though  the  emulsion  was  not  appreciably  broken. 

The  value  of  acid  and  salts  having  a  polyvalent  cation  has  been 
demonstrated  in  some  cases,  usually  in  connection  with  the  Minerals 
Separation  type  process.  In  this  process  there  is  greater  danger  of 
getting  too  good  an  emulsion  than  in  the  Callow  process,  and  the  value 
of  acids  and  salts  of  this  type  consists  in  their  power  of  breaking  down 
an  emulsion,  or  preventing  too  good  a  one  being  formed.  These  salts 
should  be  used  in  acid  solution,  or,  otherwise,  due  to  hydrolysis,  the 
insoluble  hydroxides  formed,  for  example,  Fe(OH)3,  and  A1(OH)3 
have  the  opposite  effect,  namely,  of  preventing  the  breaking  down  of 
the  emulsion  or  promoting  its  formation.13  Oil-emulsions  in  FeCl3 
solution,  on  standing,  give  a  yellow  flocculent  precipitate,  but  the  emul- 
sion is  not  broken.  The  mechanism  of  this  is  discussed  by  Ellis.14  In 
a  neutral,  pneumatic,  Callow  float,  such  salts  have  been  found  to  be 
harmful.  If  salts  of  iron  or  aluminum  are  present  in  the  feed-water 
then  acid  may  be  necessary  to  prevent  this  action  between  them  and 
the  oil-emulsions. 

The  value  of  alkalies  has  been  discussed  as  giving  a  better  oiling  of 
the  bubble-surface.  In  connection  with  emulsions,  however,  a  greater 
effect  can  be  ascribed  to  the  action  of  alkalies  or  salts  which  hydrolyze 
to  give  an  alkaline  reaction,  and  to  those  which  have  a  polyvalent 
anion.  If  a  neutral  ore-pulp  is  shaken  with  a  small  quantity  of  an 
oil-emulsion  it  is  found  that  the  slime  is  coagulated  with  the  emulsion 
and  settles  out,  often  leaving  the  liquid  quite  free  from  oil-emulsion. 
The  emulsion  is  not  broken,  but  simply  carried  down  with  the  floc- 
culated slime.  If  alkalies  are  used,  or  salts  such  as  last  mentioned, 
then  the  slime  is  deflocculated  in  the  great  majority  of  cases.  It  then 
settles  more  slowly,  and  when  it  has  settled  the  emulsion  is  left  free 
and  still  standing.  This  is  important,  for  now  the  emulsion  is  free  to 
function  as  it  should,  that  is,  to  give  oil  to  the  bubble-surface.  The 
ore-particles,  both  sulphide  and  gangue,  are  also  free  to  show  their  own 
behavior  toward  the  water  and  the  oil.  This  deflocculation  should,  and 
does,  result  in  a  higher  grade  concentrate  and  a  greater  and  quicker 
recovery,  since  now  no  sulphide-particles  are  coagulated  with,  or  sur- 
rounded by,  gangue-particles  that  prevent  their  flotation. 

The  use  of  lime  has  not  been  found  to  be  as  beneficial  as  that  of 
NaOH.  This  is  explained  by  the  fact  that  this  substance,  owing  to  the 


isBriggs  and  Schmidt,  Jour.  Phys.  Chem.,  19  (1915),  478. 
i*Zeit.  phys.  Chem.,  89  (1914),  149. 


222  FLOTATION 

predominating  effect  of  the  calcium  ion,  coagulates  instead  of  defloc- 
culating  the  slime,  and  hence  part  of  the  emulsion  is  removed  and  the 
individual  particles  are  not  free  to  float  as  they  should.  This  coagu- 
lating action  may  be  more  noticeable  in  a  Callow  cell  than  in  a  cell  of 
the  Minerals  Separation  type,  as  in  the  latter  the  coagulated  slime  may 
be  broken  up  considerably,  but  the  tendency  is  the  same  in  either  case. 

The  principles  involved  when  varying  quantities  of  oil  are  used,  is 
a  question  on  which  there  is  great  difference  of  opinion.  From  theory 
there  should  be  no  difference  whether  a  large  or  small  amount  of  oil  be 
used,  provided  the  oil  is  properly  emulsified.  If  a  large  amount,  2% 
or  3%,  be  used,  and  is  not  emulsified  sufficiently,  the  excess  may  float 
and  be  of  disadvantage  in  several  ways.  To  test  this  point  a  float  was 
made  with  an  amount  of  oil  equivalent  to  2%  of  the  weight  of  the  ore, 
emulsified  in  a  De  Laval  emulser,  and  added  at  the  cell  (Callow),  and 
a  float  made.  It  behaved  in  every  way  the  same  as  when  0.2%  or  less 
of  oil  was  used,  and  the  recovery  was  better,  with  as  high  a  grade  of 
concentrate.  Of  course,  economy  would  settle  the  minimum  amount  of 
oil  to  use.  This  was  repeated  with  other  oils  and  ores.  The  extra 
amount  of  oil  used  gave  a  greater  oiling  of  the  bubble-surface,  and  in 
fact  these  floats  were  better  than  when  alkali  was  used  to  make  the 
smaller  amount  of  oil  more  efficient. 

In  the  light  of  the  above  work  the  question  of  flotation  ' poisons' 
was  taken  up  with  the  idea  that  any  substance  which  will  prevent  the 
breaking  down  of  an  emulsion  or  coalescence  of  oil  droplets,  or  which 
gives  adsorption  of  colloidal  particles  at  the  oil-water  interface,  is 
harmful  to  flotation.  In  the  first  two  cases  the  proper  amount  of  oil 
will  not  be  freed,  and  in  the  other  case  the  oil-surface,  if  formed, 
would  be  covered  by  an  adsorbed  layer,  so  that  no  oil-surface  would  be 
presented  for  attachment  of  the  mineral.  Experimental  work,  by 
actual  flotation,  had  shown  what  substances,  including  many  dyes,  were 
harmful.  Solutions  of  these  substances  of  0.01%  strength  were  shaken 
in  test-tubes,  with  about  2  c.c.  of  oil,  for  a  few  minutes,  to  the  same 
extent  and  at  the  same  time.  The  tubes  were  then  placed  upright  and 
the  amount  of  emulsification  and  the  rapidity  of  coalescence  of  the  oil 
droplets  rising  to  the  top  noted,  with  the  following  results : 

(1)  Slight  or  no  emulsification  and  rapid  coalescence  of  droplets 
when  using  methylene  blue,  saffranine,  and  bismarck-brown.     These 
dull  dyes  really  act  like  salts,  and  are  not  colloidal,  nor  are  they  harm- 
ful to  flotation.    In  fact,  these  dyes  assist  slightly  in  breaking  an  emul- 
sion. 

(2)  Extremely  slow  coalescence  of  droplets,  the  finely  divided  oil 


THEORY   OF   ORE   FLOTATION  223 

layer  lasting  for  several  hours  to  days,  when  using  congo-red,  ben- 
goazurin,  azo-blue,  saponine,  tannic  acid,  waste  sulphate  liquor,  hemo- 
globin, and  eosin.  These  substances  are  all  injurious  to  flotation.  Most 
of  these  are  negative  colloids.  Hemoglobin  is  highly  colloidal,  and  posi- 
tive, and  its  adsorption  is  probably  enhanced  because  it  is  oppositely 
charged  to  the  oil-emulsion.  Several  of  this  last  class  of  substances, 
especially  saponine,  gave  marked  emulsification,  even  with  the  small 
amount  of  shaking  received.  Some  of  these  substances  also  form  quite 
stable  and  viscous  skins  at  oil-surfaces.  Another  experiment  consisted 
in  dividing  an  oil-emulsion  into  two  parts,  to  one  of  which  tannic  acid 
was  added,  and  then  frothing  over  equal  volumes  of  each  in  a  small 
cell.  The  one  to  which  tannic  acid  had  been  added  contained  3.5 
times  as  much  oil  in  the  residue  or  tail- water  as  the  other.  This  shows 
that  the  oil-emulsion  had  been  kept  from  breaking  down,  and  the  oil 
being  frothed  over.  Besides  the  substances  given  above,  the  injurious 
effect  of  insoluble  hydroxides  of  the  heavy  metals  has  been  explained 
under  emulsions.  Other  inorganic  colloids  have  been  found  to  be 
injurious,  for  example,  when  floating  with  K4Fe(CN)6,  the  Cu2Fe 
(CN)G  formed  from  the  oxidized  and  soluble  copper  hurts  the  float 
very  noticeably.  The  experimental  evidence  proves  that  the  action 
of  these  colloids  is,  without  doubt,  as  stated,  though  they  may  also 
adsorb  at  the  solid  surfaces,  and  in  that  way  cause  a  poorer  result  to 
be  obtained.  It  is  easily  seen  how  the  water  used  in  flotation  and  the 
slime  coming  from  certain  ores  have  a  great  effect  in  flotation.  This 
has  caused  some  to  say  that  it  is  the  gangue  that  determines  the  success 
of  the  process,  and  if  the  water-supply  be  included  in  this,  they  are 
to  a  certain  extent  correct. 

The  froths  produced  in  flotation  are  useful  as  a  mechanical  means 
of  removing  "the  mineral  brought  up  by  the  bubble.  The  formation  of 
a  froth,  and  its  stability,  are  due  principally  to  dissolved  materials 
in  the  water  which  give  to  the  solution  a  variable  surface-tension.  The 
static  surface  of  a  solution  has  a  lower  tension  than  a  fresh  surface, 
whether  the  substance  added  lowers  or  raises  the  surface-tension  of  the 
solvent.  Since  a  large  lowering  may  be  caused  by  a  small  amount  of 
solute  and  only  a  small  rise  may  be  obtained,  the  best  frothing  agents 
are  those  that  lower  the  surface-tension.  Pine-oil  is  used  to  a  large 
extent  for  this  purpose  in  practice,  the  soluble  portion  causing  a  con- 
siderable lowering  of  the  surface-tension  of  water.  In  many  articles 
that  have  appeared  on  the  theory  of  flotation,  it  has  been  stated  that 
oils  lower  the  surface-tension  of  water.  This  is  not  very  clearly  stated, 
since,  as  ordinarily  understood,  oil  is  insoluble  in  water,  and  only  sol- 


224  FLOTATION 

uble  material  can  affect  the  surface-tension  of  water.  Besides  the  sol- 
uble portion  of  pine-oil,  a  part  of  many  other  flotation  oil-mixtures  is 
soluble  and  gives  a  froth.  Terpineol,  menthol,  and  many  such  sub- 
stances are  powerful  frothing  agents.  The  lasting  qualities  of  a  froth, 
as  stated  above,  are  due  to  its  variable  surface-tension,  for  if  a  bubble 
starts  to  thin  out  or  to  break  at  a  certain  point  this  fresh  surface  has  a 
greater  surface-tension  than  before,  hence  is  automatically  strength- 
ened at  this  point  and  resists  rupture.  In  using  alkalies  it  is  observed 
that  a  more  quickly  breaking  froth  results  in  a  pneumatic  cell.  This 
can  be  explained  by  the  fact,  as  stated  before,  that  a  greater  extent  of 
bubble-surface  is  covered  with  oil,  hence  there  is  less  surface  which  con- 
tains only  the  adsorbed  frothing  agent,  and  since  oils  themselves  do 
not  produce  good  froths,  the  froth  breaks  more  quickly  than  when 
alkalies  are  not  used ;  or,  this  observation  may  be  used  to  support  the 
view  that  the  bubbles  are  better  oiled  in  an  alkaline  pulp.  A  froth  is 
also  stabilized  by  the  slime  present  in  a  pulp,  or  by  other  colloidal 
matter.  Colloidal  material  dissolved  in  the  oils  will  make  an  oil-froth 
more  lasting.  A  mixture  of  oils,  the  same  as  an  aqueous  solution,  gives 
a  better  froth  than  a  pure  oil. 

Considerable  weight  has  been  placed  by  many  upon  the  electro- 
static forces  that  might  be  present  in  the  flotation  process.  Some  have 
even  considered  the  attraction  that  holds  the  sulphide  to  the  bubble- 
surface  to  be  of  this  origin.  Air  bubbled  through  water  has  been  found 
to  carry  ions,15  and  from  this,  and  the  fact  that  most  substances  have 
a  contact-difference  of  potential  when  in  contact  with  water  or  solu- 
tions, an  electrical  theory  has  been  built  up,  though  in  many  cases 
serious  errors  have  been  made  regarding  the  action  of  these  forces. 
Measurements  were  made  to  determine  these  forces.  The  small  metal 
Callow  cell  used  was  grounded,  as  this  condition  prevails  in  actual 
practice.  The  charge  carried  by  the  air  issuing  from  the  flotation  pulp 
was  discharged  on  a  metal  screen  placed  above  the  cell,  and  the  effect 
measured  by  means  of  a  Dolezalek  electrometer.  The  readings  in  this 
case  are  measured  in  volts  per  minute.  The  charge  upon  the  air  from 
several  pulps  was  measured  and  in  no  case  did  it  exceed  0.011  v.  per 
minute,  and  was  usually  only  about  half  that  value.  The  air  was  nega- 
tive in  neutral  pulps,  but  slightly  positive  in  one  of  the  alkaline  pulps. 
The  charge  on  the  froth  was  also  measured,  and  this  varied  from  zero 
to  0.011  v.  as  the  maximum.  This  was  sometimes  positive,  and  under 
other  conditions  negative.  In  two  good  floating  pulps  the  froth  was  at 


Kelvin,  McLean,  and  Gait,  Proc.  Roy.  Soc.,  1894,  57;    Coehn  and 
Mozer,  Ann.  Physik,  43  (1914),  1048. 


THEORY    OF    ORE    FLOTATION 


225 


almost  zero  potential,  though  0.002  v.  could  easily  be  determined.  It 
seems,  then,  that  these  electro-static  effects  are  far  too  small  to  exert 
any  important  part  in  flotation,  and  cannot  possibly  be  the  foyce  that 
holds  the  sulphide  to  the  bubble.  This,  too,  would  require  a  dielectric 
film,  such  as  oil,  between  the  two  .oppositely  charged  bodies,  the  sul- 
phide and  the  gaseous  ions  in  the  bubble;  but  since  flotation  results 
without  the  use  of  oil  in  many  cases,  and,  without  doubt,  the  bubble- 
surfaces  are  often  not  completely  covered  by  oil  even  when  oil  is  used, 
it  seems  that  this  theory  cannot  hold.  The  contact  difference  of  poten- 
tial of  various  minerals  has  been  used  in  some  theories.  These  were 
also  measured  by  an  electro-endosmose  method  as  described  by  Perrin.1 
To  this  apparatus  a  small  calibrated  tube  was  sealed  at  the  top  of  the 
diaphragm  side,  so  that  when  dilute  electrolytes  are  used  the  gas  gen- 
erated can  be  forced  over  into  this  tube,  after  the  experiment  is  over, 
and  this  correction  applied  to  the  amount  of  liquid  apparently  trans- 
ferred through  the  powdered  material.  The  distance  between  the 
electrodes  was  12  cm.  and  the  potential  110  v.  The  results  obtained 
give  the  sign  of  the  charge  on  the  solid  in  contact  with  the  water  or 
solution,  but  quantitative  results  as  to  the  actual  potential  differences 
are  difficult  to  obtain  in  this  way.  However,  some  idea  can  be  had  by 
comparing  the  amount  of  liquid  transferred  for  the  minerals,  to  that 
transferred  in  the  case  of  silica,  whose  potential  difference  against 
water  has  been  found  by  cataphoresis  measurements.  This  is  found  to 
be  approximately  -0.042  v.  For  quartz  and  ferric  hydroxide,  see 
Whitney  and  Blake.17 '  The  results  obtained  are  as  follows : 


Mineral 

Liquid 

Sign  of 
solid 

Liquid  transferred, 
cu.  mm.  per  min. 

Silica 
Alumina 
Chalcopyrite 
Galena 
Sphalerite 
Molybdenite 
Malachite 
Malachite 
Galena 

Water 
AT/100  HC1 
Water 
Water 
Water 
Water 
Water 
2V/100  HC1 
P.  W./500  FeCl3 

Negative 
Positive 

9 

Negative 
Negative 
Negative 
Positive 
Positive 
Positive 

30.7 
40.0 
Approx.    0 
3.6 
6.1 
3.7 
4.0 
17.8 
44.3 

Here  the  sulphides  tested  are  seen  to  be  slightly  negative  against 
water,  or  practically  zero  in  the  case  of  chalcopyrite.  This  agrees  with 
our  ideas  concerning  the  contact-difference  of  potential  of  these  sub- 
stances and  with  cataphoresis  experiments  on  colloidal  sulphides,  and 


™jour.  Chem.  Phys.,  2  (1904),  601. 

.  Am.  Chem.  Soc.,  26  (1914)^1339. 


226  FLOTATION 

the  like.  Malachite  is  positive,  as  would  be  expected  from  its  basic 
character.  The  last  result  given  in  the  table  is  probably  due  to  the 
formation,  by  hydrolysis,  of  ferric  hydroxide,  and  its  adsorption  on 
the  surface  of  the  mineral,  so  that  the  action  is  exactly  the  same  as  for 
ferric  hydroxide  itself.  In  this  case  again,  no  attraction  can  exist  on 
the  basis  of  electrical  charges  between  sulphides  and  oil  in  emulsions, 
since  they  are  of  the  same  sign.  The  charges  on  oil  in  emulsions  in 
dilute  salt-solutions,  etc.,  are  given  by  Ellis,18  Powis,19  and  others. 
This,  however,  would  not  determine  the  charges  on  a  mineral  and  oil, 
if  the  two  were  in  actual  contact,  as  is  necessary  for  flotation.  The 
charges  carried  by  the  oil  in  emulsions  are  important  probably  in  con- 
nection with  positively  charged  colloids  which  act  as  poisons,  and,  of 
course,  the  coagulation  of  slime,  and  the  breaking  of  an  emulsion  by 
electrolytes,  is  a  function  of  the  charge  carried  by  them ;  but  it  is  not 
possible  to  use  these  charges  as  an  explanation  of  the  primary  princi- 
ples involved  in  flotation. 

The  following  is  a  summary  of  the  conclusions  arrived  at  as  a  result 
of  the  experiments  made : 

( 1 )  For  an  ore  particle  to  float,  it  must  be  interf acial  between  oil 
and  water,  or  it  must  go  completely  into  the  oil-phase.     If  no  oil  be 
used,  the  particle  must  be  interf  acial  between  water  and  air.    The  force 
holding  the  particle  to  the  bubble  is  much  greater  when  oil  is  used. 

(2)  In  addition  to  its  value  as  a  lifting  agent,  the  bubble  serves 
to  produce  a  large  air-surface  in  contact  with  the  pulp.    This  surface 
is  covered  to  a  greater  or  less  extent  by  an  oil-film,  to  which  the  min- 
eral may  go,  so  that  a  small  amount  of  oil  is  very  efficient. 

(3)  The  oil  should  not  be  so  well  emulsified  that  it  will  not  be 
given  up  to  the  bubble-surface ;  and  yet  should  be  sufficiently  emulsi- 
fied, in  a  pneumatic  process,  to  last  during  the  time  of  floating. 

(4)  Colloids  in  general  are  harmful,  owing  either  to  their  causing 
too  stable  an  emulsion,  or  to  their  adsorption  on  the  oil-film  at  the 
bubble-surface,  preventing  mineral  attachment.     This  is  the  action  of 
the  so-called  '  flotation  poisons. ' 

(5)  The  froth  formed  is  attributable  either  to  the  soluble  portion 
of  the  flotation  mixture,  which  produces  a  variable  surface-tension,  or 
to  finely  divided  or  colloidal  materials. 

(6)  Acids,  alkalies,  and  salts  affect  all  these  factors. 

(7)  The  electrical  effects,  other  than  the  colloidal  charges,  are  not 
important  in  flotation. 


it.  phys.  Chem.,  78  (1911),  325. 
.,  89  (1914),  91. 


THEORY    OF    ORE    FLOTATION  227 

(8)  The  nature  of  the  solid-surface,  in  relation  to  its  wetting 
properties,  has  been  discussed  and  an  explanation  of  the  'hysteresis' 
of  the  contact-angle  advanced. 

In  the  light  of  present  knowledge  it  is  impossible  to  measure  many 
of  the  forces  operative  in  flotation,  such,  for  example,  as  the  interf acial 
tensions  between  solids  and  liquids,  or  to  explain  the  mechanism  of 
adhesion.  Such  problems  are,  however,  nearer  solution,  due  to  the 
material  advances  made  recently  by  Laue20,  and  by  Bragg  and  Bragg,21 
by  which  the  actual  arrangement  of  the  atoms  in  a  crystal  may  be  de- 
termined, and  also  by  Langmuir,22  whose  work  on  the  constitution  of 
solids  and  liquids,  the  structure  of  solid-surfaces,  and  the  mechanism 
of  adsorption,  leads  toward  an  understanding  of  these  obscure  phe- 
nomena. 


THE  RECOVERY  that  it  is  possible  to  effect  in  a  flotation  plant  de- 
pends largely  on  the  grade  of  concentrate  desired.  With  a  low  grade 
of  concentrate,  a  low  tailing  can  be  made,  but  when  a  high  grade  of 
concentrate  is  stipulated,  increased  tailing-losses  cannot  be  avoided. 
A  question  that  suggests  itself  in  this  connection,  and  which  we  have 
tried  to  answer  by  laboratory  experiments  is,  "How  can  we  raise  the 
grade  of  our  concentrate — that  is,  reduce  the  percentage  of  insoluble 
matter  contained — without  entailing  additional  copper  losses?"  We 
know  from  laboratory  experiments  that  this  can  be  done  by  expensive 
methods — for  instance,  by  heating  the  solutions — but  such  a  procedure 
would  be  undesirable  from  an  economical  standpoint.  Experience  has 
shown  us  that  concentrate  produced  in  the  first  compartments  of  the 
cleaner-cells  is  always  freer  from  insoluble  matter  than  the  concen- 
trate produced  in  the  last  compartments.  The  problem  then  resolves 
itself  into  finding  a  suitable  cleaning  process  for  the  concentrate  from 
the  last  compartments  of  the  cleaning-cells.  By  treating  this  low- 
grade  concentrate  hot,  with  the  addition  of  caustic  soda,  we  have  been 
able  to  separate  it  into  a  high-grade  concentrate  and  a  fairly  low 
tailing.  This  method  necessitates  only  the  expense  of  heating  a  small 
fraction  of  the  pulp  and  may  be  a  commercial  possibility. — Rudolf 
Gahl,  Trans.  A.  I.  M.  E. 


.  Akad.  Wiss.,  Wein,  June  1912. 
2iProc.    Camb.   Phil.   Soc.,   17    (1912),   43;    and   treatise   on   'X-Rays   and 
Crystal  Structure.' 

22/owr.  Am.  Chem.  Soc.,  38  (1916),  2221. 


228  FLOTATION 


FLOTATION  AT  THE   CALAVERAS   COPPER— A  SIMPLE 

FLOW-SHEET 

By  HALLETT  E.  ROBBINS 
(From  the  Mining  and  Scientific  Press  of  November  25,  1916) 

INTRODUCTION.  The  Union  mine  is  situated  in  the  foot-hills  of  the 
Sierra  Nevada  in  the  extreme  southern  part  of  Calaveras  county, 
California.  The  town  of  Copperopolis,  with  a  present  population  of 
about  600,  has  grown  up  around  the  mine,  and  is  reached  by  road 
from  Angels  Camp,  12  miles ;  Stockton,  42  miles ;  or  Milton,  17  miles. 
The  mail  is  carried  by  automobile-stage  daily  except  Sunday  over  the 
last  route,  and  there  is  also  regular  auto-stage  service  from  Stockton. 
Surveys  have  just  been  completed,  and  construction  is  about  to  be 
started,  on  an  extension  of  the  Southern  Pacific  railroad  from  Milton 
to  Copperopolis. 

This  is  one  of  the  oldest  and  most  interesting  metal  mines  in  Cali- 
fornia. It  was  discovered  by  placer  miners  in  1859,  and  soon  after- 
ward one  portion  of  the  lode  was  acquired  by  Frederick  Ames  of 
Boston,  and  another,  called  the  Keystone  mine,  by  Oliver  Ames.  The 
Union  Copper  Mining  Co.,  organized  by  the  former,  subsequently 
absorbed  the  Keystone  property,  as  well  as  several  smaller  holdings 
on  other  portions  of  the  lode.  Operations  Avere  conducted  by  the 
Union  Copper  Mining  Co.  on  a  large  scale.  During  each,  of  the  years 
1865  and  1866  about  23,000  tons  of  ore,  averaging  over  20%  copper, 
was  shipped  to  Swansea,  by  wagon  to  Stockton,  by  river-boat  to  San 
Francisco  bay,  and  finally  by  sailing-vessel  around  the  Horn.  A  stone 
blast-furnace  was  erected  and  operated  on  second-class  ore  averaging 
10%  copper,  using  charcoal  as  fuel.  The  matte  was  shipped  to 
Swansea.  No  statistics  are  available  as  to  the  tonnage  treated  in  this 
smelter. 

The  fall  in  the  price  of  copper  following  the  Civil  War,  as  well  as 
the  high  cost  of  transportation,  caused  the  mine  to  be  closed-down 
in  1867,  in  which  condition  it  remained  until  1887,  when  there  was  a 
renewal  of  activity  at  the  property,  culminating  in  the  erection,  in 
1891,  of  another  blast-furnace  smelting-plant,  which  ran  about  two 
years,  and  produced  150,000  tons  of  slag. 

Operations  were  again  suspended  in  1893,  the  mine  remaining  idle 
until  1905,  when  a  gravity-concentration  mill  and  a  third  smelter 
were  built.  The  mill  did  not  run  longer  than  a  week  or  two  at  this 


FLOTATION    AT    CALAVEKAS    COLTER 


229 


period,  but  the  smelter  ran  about  two  years  on  first-class  ore.  Heap- 
roasting  was  practised,  the  calcine  being  smelted  in  a  50  by  7  ft. 
reverberatory  furnace,  producing  a  50%  matte,  which  was  shipped  to 
a  refinery  at  Chicago. 

The  panic  of  1907  caused  another  suspension  of  operations,  lasting 
until  1909,  when  the  Calaveras  Copper  Co.  was  organized  and  took 
over  the  property  on  a  bond.  The  smelter  was  re-built,  and  two 
20-ft.  six-hearth  McDougall  roasters  were  erected.  The  plant  proved 

CRUSHING-PLANT 

3-iuch  product 

3500-ft.   ELECTRIC   TRAMWAY 
ORE-BIN 


1  l.y  G.ft.  A-C.  BALL  MILL 
Product  (40%  through  80  inosh) 

STANDARD  DUPLEX  DORR  CLASSIFIER 

f  | > 

Sand  Overflow  (90%  through  80  mesh. 

4  PNEUMATIC  FLOTATION  CELLS  IN   PARALLEL 


Krlth 


Underflow 


*~~                                ~~\ 

BUCKET-ELEVATOR 

2  PNEUMATIC  CELLS  IN  PARALLEL 
1 

22  by  10-f 

1 
Froth 

.  DORR  THICKENER 

|        > 

1 

Underflow 
f            « 

4  PNEUMATIC  CELLS  IN  PARALLEL 

Spigot  (60%  solids) 
8  ft.  OLIVER  FILTER 

Overflow 

-)*-, 

MILL-TANK 

1         C                      *             1 
Underflow                                  Froth 

TAILING  TO  WASTE 

1     *                 *           1 

Cake   (13%  moisture)               Filtra 

CONCENTRATE-BINS 

FlG.    1.      FLOW-SHEET   OF   CALAVERAS    COPPER   MILL 

unworkable  after  two  weeks'  trial,  and  then  a  40  by  120-in.  blast- 
furnace was  built,  but  it  ran  for  two  weeks  only.  Converting  equip- 
ment was  purchased  and  delivered,  but  never  installed.  The  mill  was 
operated  intermittently  at  this  time,  but  did  not  make. over  a  50% 
saving. 

In  September  1914  a  capable  and  efficient  manager  in  the  person 
of  S.  M.  Levy,  of  Salt  Lake  City,  was  appointed,  under  whose  guid- 
ance, with  the  assistance  of  E.  C.  Trask,  mill  foreman,  D.  C.  Williams, 
mine  foreman,  and  Frank  W.  Royer,  consulting  engineer,  the  property 


230  FLOTATION 

(has  been  firmly  placed  on  a  paying  basis,  and  has  become  one  of 
great  promise. 

THE  OREBODY  is  a  replacement  in  amphibolite  schist ;  it  is  from 
100  to  200  ft.  wide,  with  slate  hanging  wall  and  serpentine  foot-wall. 
The  valuable  minerals  are  chalcopyrite,  containing  no  gold  or  silver, 
and,  near  the  surface,  red  and  black  oxides  of  copper.  The  lode  is  free 
from  serious  faulting,  it  strikes  north-west,  dips  61°  north-east,  has 
been  fully  developed  for  a  length  of  1500  ft.  and  to  a  depth  of  800 
ft.,  and  is  known  to  persist  over  a  length  of  three-quarters  of  a  mile. 
There  is  every  indication  of  persistence  in  depth,  as  well  as  to  a 
greater  distance  along  the  strike. 

The  most  striking  peculiarity  of  the  ore  is  the  association  of  a 
large  amount  of  barren  pyrite  with  the  chalcopyrite.  This  is  the 
explanation  for  the  many  failures  to  exploit  the  mine,  for  when 
gravity  concentration  was  attempted,  the  pyrite  was  saved,  while  the 
chalcopyrite  was  largely  slimed  and  lost. 

THE  MINE  is  opened  by  two  working-shafts,  the  Union  and  the 
Discovery.  The  former  is  800  ft.  deep,  vertical  to  the  5th  level,  and 
on  an  incline  of  63°,  following  the  lode,  from  there  to  the  bottom. 
It  was  sunk  in  the  'sixties,  and  is  equipped  with  a  wooden  head-frame, 
35  ft.  high,  and  with  a  double-drum  hoist  with  both  steam  and  electric 
drive. 

The  Discovery  shaft  is  in  the  lode,  on  the  hanging-wall  side,  and 
is  now  400  ft.  deep,  measured  along  the  61°  incline,  but  is  being 
connected  with  the  9th  level  by  raising.  It  is  equipped  with  an  ex- 
cellent steel  head-frame,  80  ft.  high,  erected  in  1902  at  a  cost  of 
$10,000,  and  good  for  four  compartments,  though  the  shaft  now  has 
but  three ;  and  with  a  steam-driven  double-drum  hoist,  good  for  1500 
ft.,  and  with  a  1500-cu.  ft.  compressor  driven  by  a  275-hp.  motor. 

The  stopes  are  15  to  30  ft.  wide ;  the  shrinkage  method  is  followed, 
at  a  cost  of  50  cents  per  ton.  The  total  cost  of  mining,  including 
timbering,  hoisting,  development,  etc.,  with  the  present  daily  produc- 
tion of  200  tons,  is  $1.50  per  ton.  It  is  expected  that  this  will  be 
reduced  to  $1.25,  as  soon  as  the  production  is  increased  to  500  tons 
per  day,  which  is  the  maximum  output  expected  at  present. 

The  force  employed  includes  2  shift-bosses  at  $4;  10  machine- 
miners  at  $3.50;  4  timber-men  at  $3.50;  4  timber-men's  helpers  at 
$3.25 ;  and  22  shovelers  at  $2.75. 

Ingersoll-Rand  stopers  are  used  for  stoping  and  raising;  jack- 
hammers  for  sinking  and  block-holing;  and  Denver  Dreadnought 
water-drills  in  the  drifts. 


FLOTATION    AT    CALAVERAS    COPPER  231 

The  mine  is  considerably  wetter  in  winter  than  in  summer.  In  the 
wet  season,  one  4J  by  7-in.  triplex  pump  is  operated  24  hours  daily, 
raising  all  the  water  made  by  the  mine,  from  the  8th  level  to  the  sur- 
face. In  the  summer  it  is  run  only  six  to  seven  hours  per  day. 

FLOTATION.  Experiments  began  in  December  1914;  in  February 
1915,  the  so-called  'little  mill'  was  started  on  accumulated  tailing  from 


FlG.    2.      AIR-PANS    OF   FLOTATION-CELL 

the  old  gravity-mill,  containing  about  1.5%  copper.  The  equipment 
consisted  of  one  Huntington  mill,  grinding  through  50-mesh;  a  me- 
chanical agitator ;  a  pneumatic  flotation-cell,  making  a  final  tailing  and 
a  rough  concentrate ;  and  a  Wilfley  table,  making  a  final  concentrate 
and  a  middling  that  was  returned  to  the  Huntington.  In  May  1915, 
the  treatment  of  accumulated  tailing  was  discontinued,  the  'little  mill' 
after  that  date  handling  25  tons  per  day  of  undersize  from  the  1-in. 
trommel  at  the  picking-plant.  The  oversize,  after  the  first-class  ore 
had  been  picked  out,  was  treated  in  the  'big  mill,'  which  was  the  old 
gravity-mill  with  some  experimental  flotation  equipment,  handling 
60  tons  per  day,  with  much  the  same  flow-sheet  as  in  the  little  mill, 
so  that  further  description  is  not  necessary. 

The  results  of  this  operation  indicated  that  from  a  mill-feed  assay- 
ing 3%  copper,  28%  iron,  20%,  sulphur,  20%  silica,  and  10%  alumina, 
there  would  be  obtained  a  concentrate  assaying  about  19%  copper, 
30%  iron,  35%  sulphur,  and  6%  insoluble,  with  a  ratio  of  concentra- 
tion of  7 : 1,  and  a  recovery  of  90%. 

These  operations  also  indicated  that  the  most  efficient  oil  was 


232  FLOTATION 

Yaryan  steam  pine-oil,   and  that  mechanical  agitation  of  the  pulp 
before  flotation  was  necessary  for  the  best  results. 

The  old  gravity-mill,  which  was  housed  in  a  well-built  and  sub- 
stantial steel-frame  building,  was  then  further  re-modeled,  and  in 
March  1916  operations  began  according  to  the  flow-sheet  shown  in 
Fig.  1.  These  operations  have  been  remarkably  successful. 

PRESENT  PRACTICE.  The  extreme  simplicity  of  the  plant,  and  the 
entire  absence  of  any  gravity  concentration  are  very  striking.  The 
ball-mill  has  a  normal  capacity  of  about  8  to  9  tons  per  hour.  The 
reduction  in  one  mill  from  3-in.  to  a  product  90%  of  which  passes 
80-mesh  would  not  be  economical  in  a  large  plant,  but  in  a  small  one 
the  simplicity  of  the  arrangement  is  commendable.  The  mill  is  driven 
through  a  counter-shaft,  by  a  150-hp.  motor,  at  a  speed  of  23  r.p.m. 
The  normal  power  consumption  when  running  is  120  hp.  Forged  steel 
balls,  5  in.  diam.,  are  used,  the  consumption  being  0.5  Ib.  per  ton  of  ore 
ground.  Of  the  total  product  40%  is  finished  through  80-mesh,  the 
remainder  being  returned  by  the  classifier.  The  mill  has  given 
reasonable  satisfaction,  the  most  serious  difficulties  being  blinding  of 
the  difficultly-accessible  grating,  leakage  around  lining-bolt  holes  and 
dropping-out  of  lining-bolts,  and  a  peculiar  ailment,  not  as  yet  fully 
diagnosed,  but  probably  due  in  part  to  the  wear  of  the  lining,  that  at 
times  has  caused  the  capacity  of  the  mill  to  drop  practically  to  zero. 
When  the  mill  was  opened  on  such  occasions  the  ore  and  balls  were 
found  in  quite  separate  masses.  Increasing  the  speed  from  21  r.p.m., 
as  recommended  by  the  makers,  to  23  r.p.m.  proved  beneficial  in 
minimizing  this  trouble. 

Difficulty  has  also  been  encountered  in  the  buckling  of  the  lining- 
segments,  which  are  the  full  length  of  the  mill,  thicker  on  one  edge 
than  on  the  other,  in  order  to  form  steps  to  lift  the  balls  and  cause 
them  to  cascade  properly  through  the  charge  of  ore.  They  are  held 
by  three  bolts  in  a  line  along  the  centre  of  each  segment.  The  edges 
of  the  segments  draw  away  from  the  shell,  and  the  lining  requires  to 
be  discarded  and  renewed  when  only  about  half  the  metal^has  been 
worn  away.  Similar  troubles  have  been  reported  at  other  plants,  and 
it  is  my  belief  that  they  may  be  overcome  by  the  use  of  lining  in  full 
annular  sections,  wedged  in  place,  with  no  bolt-holes  whatever  through 
the  shell.  Such  sections  may  be  secured  from  the  Lehigh  Car  Wheel 
&  Axle  Co.,  and  are  being  tried  by  the  Utah  Copper  company. 

The  oil  adopted  as  standard  in  the  present  operation,  after  ex- 
haustive experiments,  is  the  No.  400  crude  wood-creosote  produced  by 
the  Pensacola  Tar  &  Turpentine  Co.  The  No.  350  crude  pine-oil 


FLOTATION    AT    CALAVERAS    COPPER 


233 


produced  by  the  same  company  was  recently  tried  on  a  24-hours  run, 
with  a  marked  increase  in  the  value  of  the  tailing,  and  a  decrease  in 
the  grade  of  the  concentrate.  A  mixture  of  equal  parts  of  No.  1 7 


FIG.    3.       THE   CALAVERAS    COPPER    MILL 


hardwood-creosote,  and  No.  20  coal-tar  creosote,  furnished  by  the 
General  Naval  Stores  Co.,  has  given  the  best  results  of  any  oil  other 
than  that  regularly  used. 

The  oil  is  all  fed  into  the  ball-mill  feed-box  from  a  15-gal.  zerolene 
can,  fitted  with  a  special  bronze  stop-cock.    The  consumption  averages 


234  FLOTATION 

0.3  lb.  per  ton  of  ore.  It  is  so  well  mixed  and  agitated  in  the  ball-mill 
that  neither  mechanical  nor  pneumatic  agitation  before  flotation  is 
found  of  any  benefit  whatever. 

The  return  of  the  filtrate  from  the  concentrate-filter,  and  of  the 
overflow  from  the  concentrate-thickener  has  been  found  not  only  to 
decrease  the  amount  of  oil  required,  but  also  to  effect  a  closer  saving 
than  is  possible  otherwise,  no  matter  how  much  oil  be  used. 

The  flotation-cells  are  made  locally  from  Oregon  fir,  protected  with 
P.  &  B.  paint,  at  a  cost  of  about  $100  each,  complete.  They  are  of  the 
type  for  which  J.  M.  Callow  has  had  process  and  apparatus  patent 
applications  pending  in  the  United  States  for  some  time.  The  porous 
bottom  differs  from  that  used  by  Mr.  Callow  in  the  cells  he  has  built. 
It  is  composed  of  eight  separate  shallow  cast-iron  pans,  placed  side 
by  side  along  the  sloping  bottom  of  the  cell,  each  covered  with  a 
multiple-ply  canvas,  fastened  around  the  edges  only.  Screens  or  grids, 
similar  to  those  used  by  Mr.  Callow,  were  tried  but  proved  both  un- 
necessary and  objectionable. 

The  outside  length  of  each  pan  is  a  trifle  less  than  the  inside  width 
of  the  cell.  Two  j-in.  pipes  are  screwed  into  the  bottom  of  each  pan, 
and  pass  through  holes  bored  in  the  wooden  floor  of  the  cell.  One  is 
connected  by  means  of  an  easily-removable  length  of  hose,  to  the  air- 
main  manifold,  and  the  other  is  fitted  with  a  plug-cock,  normally 
closed,  but  opened  periodically  to  blow  out  accumulations  of  water 
in  the  pan. 

"When  it  is  desired  to  remove  a  pan,  the  air-hose  is  disconnected, 
and  the  plug-cock  unscrewed,  when  the  pan  may  easily  be  lifted  from 
the  cell.  When  the  cell  is  in  operation,  the  holes  through  which  the 
air  and  water  blow-off  pipes  pass,  are  caulked  with  oakum.  This  form 
of  air-pan  was  an  original  development  at  Copperopolis,  but  resembles 
that  developed  previously  at  McGill,  Nevada,  and  used  in  the  pneu- 
matic flotation-cells  of  the  Nevada  Consolidated  Copper  Co.  A  photo- 
graph of  two  of  the  Copperopolis  air-pans,  one  right-side  up  and  the 
other  bottom  up,  is  shown  in  Fig.  2. 

A  detail  drawing  of  the  flotation-cell  as  a  whole,  from  which  one 
may  be  built  by  any  competent  carpenter,  is  shown  in  Fig.  4. 

Air  is  furnished  at  5J  lb.  pressure  by  a  Connersville  blower.  The 
consumption  is  about  80  cu.  ft.  free  air  per  min.  per  cell.  Each  cell  is 
emptied  once  per  day  and  the  surface  of  the  canvas  is  washed  off  with 
a  hose.  The  canvas  lasts  several  weeks,  and  when  a  renewal  is  neces- 
sary, it  is  effected  quickly  by  removing  the  pan  in  the  manner  de- 
scribed, and  replacing  it  with  one  already  freshly  clothed. 


FLOTATION    AT    CALAVERAS    COPPER 


235 


•-.--jj-^--..- -  ^.^-^-  -^--j,--^^-^.!---^^ 


236  FLOTATION 

The  air-supply  is  not  filtered,  but  I  believe  it  is  good  practice  to  do 
so  in  all  cases  where  porous  media  are  used  in  flotation-cells.  During 
the  past  two  years  I  have  visited  nearly  every  flotation  plant  of  conse- 
quence in  the  West,  and  have  seen  no  pneumatic  cell  frothing  so 
smoothly  and  evenly  as  those  at  Copperopolis. 

Some  interesting  experiments  have  been  made  in  heating  the 
thickened  concentrate  in  the  filter.  At  some  plants  where  this  has 
been  tried,  it  was  found  possible  to  make  a  cake  of  double  or  treble 
the  usual  thickness,  with  no  increase  in  the  moisture  content.  This  is 
probably  due  to  the  heat  decreasing  the  viscosity  of  the  oil  in  the  pores 
of  the  filter-canvas, 

The  results  of  the  operation  of  the  plant  may  be  appreciated  from 
the  following  assays  of  composite  samples  for  the  month  of  June  1916  : 

Copper,  %         Iron,  %         Insoluble,  % 

Heading 2.15  20.4  37.0 

Concentrate     14.40  29.5  14.9 

Tailing    0.09  18.0  43.4 

Rough  concentrate    8.0  ...  J  ....V. 

Cleaner  tailing 2.0 

Ratio  of  concentration,  7:1. 

Saving  of  copper,  96.4'/r. 

Saving  of  iron,  30.2%. 

It  will  be  interesting  to  compare  these  results  with  those  obtained 
in  the  old  gravity-mill,  the  concentrate  from  which  assayed  5.8% 
copper,  35.5%  iron,  37.4%  sulphur,  12.7%  silica,  and  6.5%  alumina. 
The  heading  ran  2.4%  copper,  the  tailing  1.5%,  the  ratio  of  concentra- 
tion was  6.6 : 1,  and  the  percentage  of  recovery  of  the  copper  was  50. 

At  present  the  tailing  normally  assays  a  'trace,'  which  means  not 
over  0.04%  copper,  a  remarkable  record,  but  I  believe  that  any  ordi- 
nary chalcopyrite  ore  may  be  treated  by  a  similar  method  with  similar 
results.  I  have  myself  made  a  mill-run  at  this  plant  with  an  ore  con- 
taining 1.38%  copper  as  chalcopyrite,  arid  22%  iron,  mostly  as 
pyrrhotite.  The  grade  of  the  concentrate  was  7.32%  copper,  the 
tailing  0.07%,  the  ratio  of  concentration  5.53:1,  and  the  recovery 
95.9%.  I  have  in  mind  two  plants  operating  under  license  from 
Minerals  Separation,  treating  simple  chalcopyrite  ores,  that  do  not 
contain  nearly  so  much  pyrite  as  the  Calaveras  ore  and  therefore 
should  be  much  easier  to  concentrate.  Each  of  these  plants  uses  a 
more  complicated  flow-sheet  than  the  Copperopolis  plant,  and  is  proud 
of  a  tailing  containing  0.15%  copper.  This  is  eloquent  evidence  con- 
cerning benefits  accruing  to  licensees  of  Minerals  Separation  from  the 
superior  ( ?)  metallurgical  knowledge  placed  at  their  disposal  by  that 
syndicate. 


FLOTATION    AT    CALAVERAS    COPPER  237 

OPERATING  COSTS.  These  are  shown  by  the  following  figures  taken 
at  random  from  the  company 's  books,  representing  actual  costs  for  the 
week  ended  July  7,  1916 : 

Power,  184  hp.  per  day,  at  0.825c.  per  kw-hr $191.25 

Operating  labor,  70  shifts,  at  $3.25 228.75 

Superintendence,  repair,  and  extra  labor 137.48 

Supplies  of  all  kinds 132.40 


$689.88 

On  a  normal  tonnage  of  192  per  day,  this  is  equivalent  to  51. 4c. 
per  ton. 

TRANSPORTATION.  Incoming  supplies  and  outgoing  concentrate  are 
hauled  between  Milton  and  Copperopolis  by  wagon  with  trailers, 
drawn  by  14  horses,  and  carrying  about  12  tons  per  load,  at  a  contract 
price  of  $3.25  per  ton,  or  about  20c.  per  ton-mile.  The  road  is  very 
rough,  and  attempts  to  use  auto-trucks  have  resulted  in  failure  thus 
far.  During  the  rainy  season  the  condition  of  the  road  is  so  bad  that  it 
is  impossible  to  do  any  hauling ;  it  has  been  necessary  even  to  suspend 
operations  during  that  period.  Rail-freight  on  the  concentrate  is 
$1.25  per  ton  from  Milton  to  the  smelter  on  San  Francisco  bay,  and 
$6.40  per  ton  to  Tacoma,  where  this  product  is  now  shipped. 

FUTURE  OPERATIONS.  There  has  just  been  installed  an  8-ft.  by 
30-in.  Hardinge  ball-mill  on  trial,  under  a  guarantee  by  its  manu- 
facturer that  it  will  grind  25%  more  ore,  with  25%  less  power  than  the 
7  by  6-ft.  Allis- Chalmers  mill.  It  should  be  remarked,  however,  that 
the  price  of  the  Hardinge  mill  is  $1800  more  than  that  of  the  Allis- 
Chalmers. 

.The  two  ball-mills  together,  whether  operated  in  series  or  in 
parallel,  are  expected  to  have  a  capacity  of  about  500  tons  per  day, 
and  10  additional  flotation-cells,  with  the  necessary  blower,  are  being 
installed  to  take  care  of  the  increased  tonnage.  The  present  Oliver 
filter  (8-ft.  diam.  by  6-ft.  face)  is  to  be  supplemented  by  one  of  the 
same  face  but  11^  ft.  diameter.  This  is  expected  to  handle  50  tons  per 
day  of  thickened  concentrate,  reducing  the  moisture  to  about  12%, 
with  a  cake  half  an  inch  thick. 

It  is  proposed  to  convey  the  concentrate  from  the  thickener  to  the 
filter  in  a  5-in.  pipe  through  the  centre  of  which  there  will  be  a  1-in. 
steam-pipe.  This  will  avoid  diluting  the  thickened  concentrate-pulp 
by  condensed  steam. 

It  is  estimated  that  no  more  labor  will  be  required  to  operate  the 
plant  when  treating  500  tons  than  at  present.  Assuming  the  power 


238  FLOTATION 

and  supply   costs  to  increase   proportionally   with   the   tonnage,   an 
average  weekly  cost  would  be  approximately  as  follows: 

Power,  479  hp.  per  day,  at  0.825c.  per  kw-hr $497 

Labor,  as  at  present 366 

Supplies     690 


$1553 

This  is  equivalent  to  44.4c.  per  ton,  but  it  is  believed  the  actual 
cost  will  not  exceed  40c.  On  the  completion  of  the  railroad,  the 
capacity  of  the  plant  may  be  still  further  increased  by  the  installation 
of  a  third  ball-mill,  for  which  room  is  yet  available  in  the  old  mill- 
building. 

The  total  capital  expenditure  for  converting  the  old  gravity-mill 
into  a  highly  efficient  flotation-mill  of  500  tons  daily  capacity  will  be 
less  than  $50,000.  A  new  mill  built  according  to  this  flow-sheet  should 
not  cost  much,  if  any,  more,  as  the  figure  noted  includes  the  net  cost  of 
considerable  experimenting,  and  the  dismantling  of  the  entire  equip- 
ment of  the  old  mill,  amounting  to  as  much  as  a  new  building  would 
cost  under  ordinary  circumstances. 

Without  wishing  to  draw  invidious  comparisons,  it  is  interesting 
to  note  that  the  National  mill  in  the  Coeur  d'Alene,  built  to  treat  500 
tons  per  day  of  a  simple  chalcopyrite  ore,  cost  $153,000,  and  has  never 
made  so  close  a  saving  as  the  Calaveras  plant,  and  cost  about  the  same 
to  operate  as  the  latter  with  its  present  small  capacity  of  less  than 
200  tons  per  day.  Of  course,  much  less  was  known  about  flotation 
when  the  National  mill  was  built  than  today. 

Messrs.  Levy  and  Trask  are  modest  as  to  their  achievements,  but 
rumors  of  the  excellent  results  they  have  accomplished  have  traveled 
widely,  and  the  plant  has  been  a  Mecca  for  metallurgists  from  all 
parts  of  the  country.  Each  visitor  has  departed  with  a  pleasant  im- 
pression of  the  courtesy  with  which  he  was  received  and  the  freedom 
with  which  all  desired  information  was  made  available. 


COLLID  describes  a  state  and  not  a  form  of  matter.  See  Robert  J. 
Anderson  in  this  volume.  He  also  explains  the  difference  between 
'adsorption'  and  ' absorption',  questioning  the  idea  that  the  release 
of  air  or  other  gases  occluded  by  minerals  can  be  a  factor  in  flotation. 


THE   HORWOOD   PROCESS  289 

THE  HORWOOD  PROCESS  OF  FLOTATION 

By  ALLAN  D.  RAIN 
(From  the  Mining  and  Scientific  Press  of  October  7,  1916) 

*The  Horwood  process  bears  the  name  of  its  originator,  E.  J. 
Horwood,  assistant  general  manager  for  the  Broken  .Hill  Proprietary 
Company,  at  Broken  Hill,  Australia.  Briefly,  the  principle  of  the 
process  as  applied  to  mixed  lead-zinc  sulphide  ores  is  that  advantage 
is  taken  of  the  different  oxidizing  temperatures  of  galena  and  blende, 
the  galena  oxidizing  to  lead  sulphate  much  quicker,  that  is,  at  a  much 
lower  temperature  than  the  blende  oxidizes  to  zinc  sulphate  (given,  of 
course,  the  ore  of  a  fineness  that  is  necessary  for  separation  of  the 
lead  and  zinc  particles).  Such  being  the  case,  by  judicious  roasting 
of  a  mixture  of  these  two  minerals  the  lead  sulphide  can  be  totally  or 
superficially  oxidized  to  its  sulphate  under  control  temperature  with- 
out affecting  the  zinc  sulphide.  By  a  subsequent  flotation  operation, 
the  blende  may  be  recovered  in  the  ordinary  way  and  the  lead  sulphate 
or  the  sulphide  coated  with  a  film  of  the  sulphate  that,  not  being 
amenable  to  flotation,  remains  as  a  residue.  It  may  be  better,  before 
dealing  with  the  process  on  a  commercial  scale,  to  give  a  description 
of  the  method  of  making  laboratory  tests. 

PREPARATION  OF  THE  ORE.  On  all  ores  treated  to  date,  it  has  been 
found  that  the  material  must  be  screened  through  an  80-mesh  sieve. 
Generally  speaking,  this  ought  to  be  considered  the  maximum  of 
coarseness,  and  for  close  recoveries  of  either  zinc  or  lead,  the  finer  the 
material  the  better  for  the  process. 

SULPHATIZATION.  The  success  of  the  process  depends  on  the 
manner  in  which  this  is  done,  the  object  being  to  preferentially  sul- 
phatize  the  galena,  leaving  the  blende  unchanged.  By  keeping  the  ore 
at  a  low  ^temperature  for  the  first  portion  of  the  roast,  and  then  rais- 
ing the  heat  toward  the  latter  portion  (provided  the  material  is  kept 
freely  stirred  the  whole  time)  no  difficulty  will  be  experienced  in  the 
laboratory,  in  changing  the  galena  and  leaving  the  blende  unaltered. 
It  is  obvious  that  at  no  time  during  the  roast  must  the  temperature  be 
raised  sufficiently  high  to  oxidize  the  blende.  Should  this  happen, 
however,  the  final  object  of  the  process  will  not  be  defeated,  but  the 


*Abstract   from    Teniente   Topics,  published  by  the  Braden   Copper   Co., 
Chile. 


240  FLOTATION 

resultant  zinc  loss  (due  to  the  solution  of  any  oxidized  compounds  in 
the  acid  used  for  subsequent  flotation)  would  be  increased.  The  in- 
creased quantity  of  zinc  thus  lost  is  directly  proportional  to  the 
amount  of  oxidized  or  sulphatized  zinc  produced  during  the  roast. 

Generally  speaking,  the  temperature  to  be  maintained  during  the 
roast  should  increase  from  400°  C.  at  the  start  to  about  500°  C.  at  the 
end.  Some  ores  require  a  longer  roast  than  others,  the  time  being 
dependent  on  the  nature  of  the  sulphides  present,  and  the  degree  of 
comminution  of  the  ore.  It  is  not  necessary  to  completely  sulphatize 
the  whole  of  the  galena  in  order  to  separate  it  from  the  blende.  The 
degree  to  which  sulphatization  should  be  carried  is  to  some  extent 
dependent  on  the  size  of  the  ore  particles.  In  order  to  deaden  the 
galena  to  flotation  it  is  sufficient  to  convert  the  surface  of  the  particles 
into  sulphate,  the  core  of  such  particles  remaining  unchanged.  The 
only  method  of  ascertaining  definitely  when  the  sulphatization  has 
been  carried  sufficiently  far  is  to  take  portions  of  the  roasted  ore  and 
make  laboratory  tests  on  them,  carefully  weighing  and  assaying  the 
products  so  obtained. 

If  laboratory  tests  are  made  prior  to  sulphatization  on  a  large 
scale,  and  the  lead  sulphate  determined  in  the  sulphatized  material, 
this  will  afford  a  simple  and  rapid  method  of  determining  when,  in 
actual  practice,  the  roast  has  been  carried  sufficiently  far.  Then,  for 
example,  assuming  that  in  the  laboratory  the  lead  sulphide  had  been 
sulphatized  to  the  extent  of  78%,  and  that  such  material  gives  the 
desired  results,  all  that  is  necessary  in  roasting  a  bulk  lot  of  ore  is  to 
withdraw  a  sample  every  quarter  of  an  hour  from  the  furnace  and 
determine  its  lead  sulphate  contents,  this  determination  not  taking 
more  than  a  few  minutes.  For  instance,  a  sample  of  zinc-lead  slime 
sulphatized  in  the  laboratory  over  a  gas-burner  for  about  two  and  a 
half  hours  was  found  to  contain  73%  lead  as  sulphate ;  the  subsequent 
separation  made  on  this  material  yielded  approximately  an  86% 
zinc  recovery  and  an  81%  lead  recovery  in  zinc  and  lead  concen- 
trates respectively.  A  small  amount  of  zinc  is  lost  invariably  in  the 
subsequent  flotation,  by  reason  of  the  formation  of  soluble  zinc  com- 
pounds during  the  roast ;  but  if  the  roast  has  been  carried  out  in  the 
correct  manner,  the  quantity  of  zinc  so  lost  should  not  amount  to 
more  than  at  most  2  to  3%  of  the  total  zinc  in  the  ore. 

FLOTATION.  Fifty  grammes  of  the  sulphatized  ore  is  weighed  and 
placed  in  a  500-e.c.  cylinder,  provided  with  a  stopper.  Boiling  water 
is  admitted  to  the  250-c.c.  mark,  then  3  c.c.  of  95%  sulphuric  acid 
(Sp.  Gr.  1.8376)  and  the  mass  is  agitated  for  a  short  time.  After 


THE    HORWOOD   PROCESS  241 

this,  either  0.1  c.c.  or  0.2  c.c.  of  oleic  acid  is  added,  and  the  whole  is 
then  thoroughly  shaken  by  hand.  The  agitation  is  continued  until 
the  sulphides  become  thoroughly  oiled  and  float  to  a  large  extent. 
The  contents  are  then  transferred  to  a  16-oz.  beaker  and  the  balk  in- 
creased with  boiling  water  that  has  been  used  to  rinse  the  cylinder. 
The  beaker  is  then  placed  on  a  sand-bath  and  flotation  is  produced 
by  heating  the  bottom  of  the  beaker.  A  little  calcite  is  added  prior  to 
the  application  of  the  heat,  to  prevent  the  material  from  lying  dead  on 
the  bottom  and  to  assist  the  flotation.  During  flotation  the  mass  in  the 
beaker  is  stirred  gently  with  a  glass  rod  in  order  to  hinder  the  forma- 
tion of  too  large  clots,  which  include  floured  lead  sulphate.  The  con- 
centrate is  removed  with  a  spoon  from  the  top  of  the  liquor,  the  skim- 
ming being  continued  until  no  more  blende  floats.  The  lead  remains 
in  the  residue  as  sulphate. 

The  concentrate  resulting  from  the  above  first  separation  is  usually 
dirty;  it  requires  to  be  re-agitated  in  a  \%  sulphuric  acid  solution 
(without  the  addition  of  any  further  oil)  and  re-floated  in  a  manner 
similar  to  the  first  separation.  The  float  concentrate  resulting  from 
this  re-agitation  is  transferred  to  a  tin-can,  dried,  the  oil  burned  off, 
and  the  residue  weighed.  The  residue  resulting  from  the  two  separa- 
tions are  bulked,  transferred  to  a  tin-can,  dried,  and  weighed. 

METHOD  OF  TREATMENT  BY  ZINC  CORPORATION.  After  a  number 
of  successful  laboratory  demonstrations,  trials  more  closely  approach- 
ing commercial  treatment  were  made  on  large  parcels,  with  encourag- 
ing results.  Almost  the  first  to  become  interested  in  this  process,  be- 
sides the  originator,  E.  J.  Horwood,  was  the  management  of  the  Zinc 
Corporation,  which  had  as  a  by-product  a  small  proportion  (roughly 
5  to  6%  of  total  concentrate  produced)  of  a  mixed  lead  and  zinc 
slime,  for  which  it  could  neither  secure  sale  nor  devise  any  means  of 
successful  separation.  This  process  was  tried  as  a  probable  solution 
of  their  metallurgical  difficulties,  and  one  by  which  they  could  sepa- 
rate into  salable  products  this  mixed  lead-zinc  slime-concentrate.  This 
they  were  stacking  with  a  view  to  some  successful  treatment  later. 
The  mixed  slime  concentrate  assayed  approximately  35%  zinc,  16.5% 
lead,  and  25  oz.  silver  per  ton. 


242  FLOTATION 


THE  DISPOSAL  OF  FLOTATION  PRODUCTS 

BY  ROBERT  S.  LEWIS 
(From  the  Mining  and  Scientific  Press  of  April  7,  1917) 

INTRODUCTION.  A  little  over  two  years  ago,  I  was  talking  with  a 
mill-man  from  a  certain  plant  where  the  flotation  process  had  recently 
been  introduced.  To  my  inquiry  regarding  the  success  of  the  flotation 
equipment,  he  replied  that,  at  first,  it  was  impossible  to  obtain  a  froth. 
Then  suddenly,  due  to  some  reason  not  understood,  froth  began  to  form 
so  rapidly  that  it  soon  ran  over  the  machines  and  piled  up  in  great 
heaps  on  the  mill-floor.  It  was  of  such  a  tough  and  lasting  nature  that 
it  would  have  been  an  excellent  substitute  for  sole-leather,  and  it  was 
practically  impossible  to  handle  the  concentrate  because  of  its  sticki- 
ness. These  statements  may  contain  some  exaggeration,  but  they  indi- 
cated that  a  mill-operator 's  troubles  might  not  cease  as  soon  as  a  froth 
was  produced.  Despite  the  improvements  that  have  been  made  in  the 
technique  of  the  flotation  process,  the  satisfactory  handling  and  dis- 
posal of  flotation  concentrate  is  still  a  very  important  problem.  In 
order  to  secure  the  latest  data  on  the  practice  of  handling  flotation 
concentrate,  a  number  of  letters  of  inquiry  were  sent  to  companies 
operating  mills  or  smelters.  Nearly  all  the  information  given  below  is 
the  result  of  this  investigation. 

DEWATERING  FLOTATION- CONCENTRATE.  This  step  is  necessary  as 
a  preliminary  to  subsequent  handling  and  metallurgical  treatment. 
The  large  amount  of  water  present  in  the  froth  must  be  reduced  greatly 
before  the  concentrate  can  be  transported  economically,  either  in  sacks 
or  in  bulk,  to  its  destination.  If  shipped  a  long  distance,  the  freight 
charge  on  the  moisture  contained  may  reach  a  considerable  figure.  The 
expense  for  unloading  wet  and  sticky  material  from  cars  is  much 
greater  than  usual.  Then,  too,  custom-smelters  often  impose  a  penalty 
for  moisture  in  excess  of  a  specified  figure.  It  is  interesting  to  note 
that  steamship  companies  refuse  to  carry  a  flotation  concentrate  that  is 
very  wet.  Such  materials  shift  so  easily  that  it  is  impossible  to  keep 
the  vessel  on  an  even  keel.  After  one  ship  had  been  lost,  due  to  shifting 
of  the  cargo,  steamship  companies  refused  to  transport  concentrate  in 
which  the  moisture  ran  over  a  stipulated  amount. 

When  the  froth  is  delicate  and  breaks  easily,  as  does  much  of  the 
froth  from  flotation-machines  using  only  air-agitation,  a  simple  treat- 
ment on  a  concentrating-table  of  the  Wilfley  type  may  give  satisfactory 


DISPOSAL   OF    FLOTATION    PRODUCTS  243 

results.  However,  it  is  generally  necessary  to  employ  some  additional 
means  to  insure  disintegration  of  the  froth.  Centrifugal  pumps  have 
been  used  with  success.  Bucket-elevators  are  fairly  efficient,  but  unless 
included  in  the  original  design  of  a  plant,  are  hardly  to  be  recom- 
mended. At  the  Utah  Apex  mill,  an  elevator  71  ft.  high  is  used  to 
assist  froth-breaking.  Head-room  and  floor-space  may  be  saved  by 
employing  a  jet  of  water  instead.  Experience  has  shown  that  a  single 
large  jet,  spreading  over  the  full  width  of  the  concentrate-launder,  is  to 
be  preferred  to  a  number  of  smaller  jets.  In  the  Daly- Judge  mill,  at 
Park  City,  Utah,  a  patent  nozzle,  known  as  the  Koerting  spray,  has 
been  found  effective  in  'killing'  froth.  After  passing  the  spray,  the 
concentrate  is  thickened  in  Callow  cones  and  is  then  treated  on  Wilfley 
tables  to  separate  the  lead  from  the  zinc.  The  objection  to  the  use  of 
sprays  is  that  the  additional  dilution  of  the  concentrate  means  so  much 
more  water  to  be  disposed  of  later.  Moreover,  where  settling-tanks  are 
employed,  any  appreciable  current  in  the  overflow  carries  out  a  con- 
siderable amount  of  the  finest  concentrate.  In  an  endeavor  to  overcome 
this  objection,  Messrs.  Cole  and  Thompson  have  devised  a  special  nozzle 
(U.  S.  patent  1,180,089,  Aug.  18,  1916),  in  which  a  gaseous  liquid, 
such  as  compressed  air  or  steam,  is  mixed  with  a  small  amount  of 
water.  The  resultant  jet  has  a  whirling  motion.  The  spray  should  be 
directed  against  the  flow  of  froth  and  at  an  angle  of  from  60  to  90° 
with  the  bottom  of  the  concentrate-launder.  This  retards  the  progress 
of  the  froth  and  gives  the  jet  more  time  in  which  to  break  it  up.  The 
nozzle  should  be  placed  at  such  a  distance  from  the  launder  as  to  allow 
the  spray  to  cover  the  entire  sectional  area. 

Settling  in  bins  or  tanks  is  a  method  of  dewatering  froth  that  has 
the  merit  of  simplicity,  although  it  has  several  disadvantages.  Some 
flotation-concentrate  is  so  fine,  all  -200  mesh  and  with  a  large  per- 
centage of  -300  mesh,  that  the  time  required  for  settling  is  prohib- 
itively long.  Where  a  large  tonnage  must  be  handled  the  size  of  the 
equipment  becomes  serious.  This  point  is  well  illustrated  in  the  case 
of  one  of  the  big  copper  concentrators.  An  estimate  showed  that  a 
number  of  concrete  tanks  20  ft.  wide,  108  ft.  long,  and  from  5  to  6 
ft.  deep  would  be  required.  The  proposed  method  of  operation  was  to 
run  the  froth  into  a  tank  until  the  overflow  should  become  contam- 
inated by  the  fine  concentrate  carried  over.  The  tank-feed  was  then 
to  be  cut  off  and  the  content  settled.  The  clear  water  was  to  be  de- 
canted and  the  concentrate  allowed  to  dry  for  a  day  or  two.  However, 
the  tanks  were  never  built,  thickeners  and  filters  being  finally  adopted. 
Tanks  may  have  either  filter  or  solid  bottoms.  In  the  first  case,  vacuum- 


244  FLOTATION 

pumps  can  be  used  to  hasten  draining.  When  solid-bottom  tanks  are 
used,  the  water  must  be  decanted  from  the  settled  concentrate,  and 
care  must  be  taken  not  to  allow  the  escape  of  the  froth,  which  almost 
invariably  accumulates  on  the  surface  of  the  water.  Unless  of  special 
design,  such  as  those  arranged  for  a  Blaisdell  excavator,  tanks  must  be 
unloaded  by  shoveling.  If  desired,  the  tanks  may  be  provided  with 
steam-pipes  to  assist  drying,  but  their  use  is  hardly  to  be  recommended. 
Spreading  the  material  out  in  a  thin  layer  on  a  drying-platform  gives 
quicker  and  better  results,  but,  in  any  case,  drying  by  steam-heat  is 
expensive.  Classifiers  of  the  Ovoca  and  Akins  type  have  been  used  for 
dewatering  concentrate.  These  are  quite  successful  on  coarse  or  gran- 
ular material  that  drains  readily. 

The  following  examples  illustrate  the  practice  of  settling  flotation- 
concentrate  in  tanks  or  bins. 

1.  The  Desloge  Consolidated  Lead  Co.,  Desloge,  Missouri,  has  been 
drying  its  lead  concentrate  to  6  or  7%  moisture  in  steel  drying-tanks, 
heated  by  steam,  and  then  loading  it  by  hand  into  unlined  box-cars. 
The  method  is  expensive,  and  the  company  will  soon  install  a  thickener 
and  filter. 

2.  Monitor  Belmont  Mining  Co.,  Belmont,  Nevada,    From  3  to  4 
tons  of  a  silicious  silver-bearing  concentrate  is  produced  per  day.    The 
concentrate  is  settled,  drained,  and  dried  on  floors  to  5%  moisture. 
It  is  then  sacked  and  hauled  to  the  railroad,  where  it  is  loaded  into 
box-cars.    The  cost  per  ton  for  draining  and  drying  is  $2.20  and  $1.22 
for  sacking.    This  method  is  not  satisfactory  and  the  present  manage- 
ment is  arranging  for  a  totally  different  method  of  handling. 

3.  Name  not  given.     About  45  tons  of  60%  zinc  concentrate,  all 
-  65  mesh,  is  handled  daily.    The  froth,  with  a  water  ratio  of  6:1,  is 
run  through  a  6-in.  pipe  into  bins.     Clear  water  is  drawn  off  between 
the  settled  concentrate  and  the  froth.     The  bins  are  of  concrete,  and 
each  holds  20  tons.     They  are  lined  with  steam-coils.     The  dried  con- 
centrate, containing  about  -12%  moisture,  is  dropped  through  doors  in 
the  bottom  of  the  bins  into  wheelbarrows  and  is  loaded  into  unlined 
box-cars.    The  cost  is  40c.  per  ton  for  drying  and  lOc.  per  ton  for  load- 
ing.    Coal  costs  $2  per  ton.     The   condensation   from  the  pipes  is 
returned  to  the  boilers.    A  filter  will  be  desirable  if  a  larger  tonnage  is 
to  be  handled. 

4.  M.  W.  Atwater,  Basin,  Montana.     About  20  tons  of  zinc  con- 
centrate is  produced  daily.     All  of  it  is  -80  mesh  and  70%  is  -150 
mesh.     The  froth,  with  a  water  ratio  of  2:1,  is  run  into  one  of  four 
bins,  each  10  by  10  ft.  and  13  ft.  high.    The  overflow,  carrying  a  small 


DISPOSAL   OP    FLOTATION    PRODUCTS  245 

proportion  of  the  concentrate,  passes  into  the  next  bin.  When  a  bin  is 
filled,  the  upper  three  feet  is  discharged  into  the  overflow-bin.  The 
concentrate  is  then  shoveled  through  the  bin-doors  directly  into  box- 
cars lined  with  muslin.  Two  men  can  load  80  dry  tons  in  8  hours. 
The  same  men  prepare  the  box-cars  for  loading  and  attend  to  the  filling 
of  the  bins.  The  concentrate  contains  from  12  to  13%  moisture  when 
loaded,  but  this  drops  to  10  or  12%  by  the  time  the  smelter  is  reached. 
As  much  as  700  tons  of  concentrate  has  been  handled  in  the  four  bins 
in  30  days.  The  method  is  satisfactory,  but  it  is  necessary  to  have  deep 
bins  and  ample  bin-space.  Cost  of  loading  is  lOc.  per  ton.  The  lining 
of  the  box-cars  costs  $2  each. 

5.  Atlas  Mining  &  Milling  Co.,  Sneffles,  Colorado.    The  concentrate 
assays  10%  silica,  20%  iron,  12%  zinc,  17%  lead,  60  oz.  silver,  and 
0.2  oz.  gold.    Fifteen  tons  is  produced  daily.    The  froth  is  treated  on 
tables,  and  the  concentrate  sent  to  50-ton  collecting-tanks,  the  overflow 
from  which  is  returned  to  the  mill-circuit.     From  the  tanks  the  con- 
centrate is  shoveled  into  small  cars  and  trammed  to  an  inclined  chute 
20  in.  wide,  18  in.  deep,  and  90  ft.  long,  having  three  steam-pipes  along 
the  bottom.     The  chute  discharges  into  a  bin  where  the  concentrate  is 
sacked.    It  is  then  hauled  to  the  railroad  and  shipped  in  box-cars  lined 
with  paper. 

6.  Mears  &  Wilfley,  Silverton,  Colorado.     The  10  tons  of  concen- 
trate made  daily  is  mostly  chalcopyrite,  and  ranges  from  80  to  150- 
mesh.    The  froth  is  run  into  settling-tanks  from  which  two  drag-belts, 
15  ft.  long  and  3  ft.  wide,  requiring  ^  hp.,  pull  the  concentrate  into  a 
bin,  from  which  it  is  loaded  into  canvas-lined  box-cars  by  means  of 
wheelbarrows.     The  concentrate  runs  20%  moisture  when  loaded,  but 
only  13%  by  the  time  the  smelter  is  reached.    The  canvas  linings  are 
sent  back  by  return-freight.    Linings  show  no  wear  after  six  months' 
use.    Cost  of  handling  is  about  35c.  per  ton. 

7.  Flotation  at  Mt.  Morgan.1    The  ore  contains  gold,  copper  pyrite, 
iron  pyrite,  and  about  70%  silica.    At  the  100-ton  testing-plant  of  this 
company,  the  flotation-concentrate  was  first  run  into  round  vats  20 
ft.  in  diameter,  10  ft.  deep,  and  constructed  with  filter-bottoms.    These 
proved  unsatisfactory,  as  the  wet  slime  kept  to  the  outside  and  did  not 
drain  well.    This  difficulty  was  finally  overcome  by  using  a  number  of 
rectangular  tanks,  9  ft.  10  in.  by  10  ft.  9  in.  and  3  ft.  deep,  with  cocoa 
matting  on  a  sand-filter  bottom.    The  froth  was  run  through  the  tanks 
in  series,  three  or  four  always  being  in  operation,  and  each  filled  with 


.  Shellshear,  Aust.  lust.  M.  E.,  June,  1916. 


246  FLOTATION 

concentrate.  The  tanks  drained  to  7  or  8%  moisture  in  24  hours  and 
the  water  was  perfectly  clear. 

8.  Britannia  Mining  &  Smelting  Co.2  The  concentrate,  assaying 
14%  copper,  26.8%  iron,  and  20.8%  silica,  is  taken  from  the  flotation- 
machines  by  a  drag-elevator  that  delivers  it  to  the  shipment-bins,  where 
the  moisture  is  reduced  from  20  to  8%  by  draining.  The  Tacoma 
smelter  draws  the  line  at  10%  moisture.  The  overflow  from  the  bins 
goes  to  tanks,  from  which  the  sediment  is  delivered  to  the  flotation- 
machines,  while  the  overflow  goes  to  Dorr  thickeners.  The  thickeners 
give  an  overflow  that  goes  to  waste  and  a  spigot  product  that  is  treated 
in  the  flotation-machines. 

At  a  mill  producing  13  tons  of  concentrate,  assaying  5%  lead, 
5%  copper,  28%  iron,  18%  silica,  with  some  gold  and  silver,  the  froth 
is  settled  and  dried  in  wooden  tanks  having  steam-coils  on  the  bottom. 
The  concentrate  is  then  shoveled  into  box-cars  that  have  been  lined 
with  paper.  Cost  is  about  18c.  for  drying,  and  23c.  for  loading,  or  a 
total  of  41c.  per  ton.  The  tanks  do  not  give  sufficient  settling-area,  and 
the  costs  are  considered  high. 

At  another  plant,  both  a  zinc  and  a  lead  concentrate  are  made.  The 
total  of  concentrates  produced  is  from  3  to  4  tons.  The  concentrate  is 
settled  in  shallow  tanks,  16  in.  and  30  in.  deep,  the  water  being  de- 
canted. Steam  is  then  turned  into  pipes  on  the  floor  of  the  tanks. 
When  the  moisture  is  reduced  to  11%,  the  concentrate  is  shoveled  into 
box-cars  lined  with  resin-sized  building  paper.  The  tanks  are  housed 
over.  Some  are  provided  with  fan-induced  draft  for  drawing  off  the 
water- vapor  and  the  rest  have  natural  draft.  The  former  are  the  more 
satisfactory.  The  cost  of  loading  is  21c.  per  ton. 

A  plant  making  24  tons  of  lead  concentrate  per  day  uses  a  Dorr 
thickener  to  remove  most  of  the  water  from  the  froth.  The  concentrate 
is  then  dried  to  the  desired  point  in  tanks  16  in.  deep  with  steam-pipes 
along  the  bottom  and  the  sides.  Steam-pressure  is  75  Ib.  per  sq.  in. 
The  concentrate  is  loaded  into  unlined  box-cars.  Cost  of  treating  is 
$1.15  per  ton.  The  method  is  not  satisfactory,  and  a  filter  will  soon  be 
installed.  This  use  of  steam  for  reducing  the  moisture-content  of  flo- 
tation-concentrate is  expensive. 

In  the  case  of  a  plant  producing  10  tons  of  concentrate  per  day, 
part  of  which  is  a  50%  zinc  product  and  the  rest  a  65%  lead  product, 
this  material  is  settled  in  flat-bottom  tanks,  the  water  is  then  decanted, 
and  the  concentrate  shoveled  onto  draining-platforms,  from  which  it 
is  loaded  into  box-cars  lined  with  felt.  The  zinc  concentrate  contains 


2T.  A.  Rickard,  M.  &  S.  P.,  Nov.  11,  1916. 


DISPOSAL  OF  FLOTATION  P.RODUCTS  247 

20%  moisture,  and  the  lead  concentrate  15%  moisture.  Cost  of  treat- 
ment is  about  20c.  per  ton.  This  method  is  only  a  temporary  expedi- 
ent ;•  thickeners  and  filter  will  soon  be  installed.  Even  though  it  could 
be  done  easily,  it  would  not  be  desirable  to  dry  the  concentrate  to  the 
point  of  dusting. 

It  is  said  that  at  the  Miami  mill,  the  concentrate  from  both  the 
flotation-machines  and  the  tables  is  run  into  round  steel  tanks  having 
filter-bottoms,  and  with  a-  central  opening  in  the  tank-bottom.  A 
vacuum-pump  accelerates  the  draining.  When  drained,  a  plug  is  re- 
moved and  the  concentrate  is  shoveled  onto  a  belt-conveyor  passing 
beneath  the  tanks.  This  conveyor  discharges  onto  another  or  cross- 
conveyor  that  loads  directly  into  box-cars. 

The  most  common  method  of  dewatering  flotation  concentrate  is  by 
the  use  of  thickeners  and  filters.  Though  this  makes  an  expensive 
equipment,  it  gives  a  rapid  and  a  fairly  positive  control  over  the 
moisture-content  of  the  finished  product.  There  is  some  accumulation 
of  froth  at  the  top  of  the  thickeners.  This  is  difficult  to  handle  and 
contaminates  the  overflow  from  the  tanks.  Unique  testimony  to  the. 
apparent  solidity  of  this  accumulation  is  found  at  one  mill  where 
'near-tragedies'  are  occasionally  enacted  because  usual  canine  per- 
spicacity fails  to  deter  inquisitive  dogs  from  attempting  to  take  short 
cuts  across  the  thickeners.  Sprays  are  sometimes  used  in  an  attempt 
to  break  up  this  froth  and  baffle-boards  may  be  employed,  either 
around  the  edge  of  the  tanks  to  protect  the  overflow,  or  at  the  centre 
and  extending  below  the  surface  of  the  water  in  the  tank.  In  the  latter 
case,  the  incoming  froth  discharges  into  the  space  within  the  boards, 
and  is  broken  up  in  passing  out  into  the  rest  of  the  tank.  The  Con- 
solidated Arizona  Copper  Co.,  at  Humboldt,  Arizona,  has  found  it 
profitable  to  send  all  the  flotation-tailing  to  thickeners,  skim  off  the 
froth,  and  add  it  to  the  regular  output. 

The  filters  used  are  generally  of  the  vacuum  type,  such  as  the  Oliver 
and  Portland,  although  the  Kelly  press,  a  pressure  type,  has  been 
installed  in  some  mills.  The  pressure-filter  has  the  advantage  that  it 
can  reduce  the  moisture  in  the  concentrate  to  a  very  low  figure,  but  it 
has  been  considered  intermittent  in  action,  costly  to  operate,  and  re- 
quires close  attendance.  However,  a  company  that  produces  a  large 
daily  tonnage  of  concentrate  has  recently  decided  to  install  Kelly 
filters.  These  presses,  of  improved  design,  were  adopted  after  a  com- 
petitive test  with  a  filter  of  the  vacuum  type.  The  vacuum-filter  has  no 
competitor  when  treating  a  concentrate  that  makes  a  thick  cake  and 
filters  easily,  but,  when  the  concentrate  is  exceedingly  fine  and  retains 


248  .          FLOTATION 

water  tenaciously,  the  capacity  of  the  filter  becomes  so  reduced  and 
the  percentage  of  moisture  left  in  the  cake  is  so  high  that  a  filter  of 
the  Kelly  type  is  to  be  preferred.  A  slight  increase  in  total  cost  of 
operation  (cost  for  labor  is  little,  if  any,  greater  than  for  the  vacuum- 
filter)  is  more  than  off-set  by  the  reduced  moisture  in  the  product. 
The  positive  action  of  the  Kelly  press  enables  it  to  handle  material  that 
cannot  be  satisfactorily  treated  on  a  filter  of  the  vacuum  type. 

In  order  to  give  sufficient  capacity  together  with  a  low  proportion 
of  moisture  in  the  cake,  the  vacuum-filter  must  have  a  feed  that -is  at 
least  50%  solid.  At  one  mill  the  moisture  in  the  material  going  to  the 
filter  must  be  held  at  the  low  figure  of  35%  in  order  to  get  satisfactory 
results.  Heating  the  pulp  in  the  filter-tank  to  about  100°  F.  or  adding 
slaked  lime  will  often  increase  the  capacity  of  the  filter.  At  the  In- 
spiration mill  Dr.  Gahl  has  plotted  the  percentage  of  silica  in  the 
concentrate  along  with  the  moisture  content  of  the  filter-cake.  A 
change  in  the  former  due  to  variations  in  the  ore,  or  in  the  operation 
of  the  plant,  is  followed  by  a  closely  corresponding  change  in  the 
latter.  This  suggests  that  the  percentage  of  silica  present  has  a  marked 
effect  on  the  dewatering  action  of  the  filter.  It  would  be  interesting  to 
know  whether  this  holds  true  in  other  plants  and  with  different  kinds 
of  concentrate. 

In  a  recent  bulletin  of  the  American  Institute  of  Mining  Engineers, 
.operation  (cost  for  labor  is  little,  if  any,  greater  than  for  the  vacuum- 
filters.  He  states:  "Our  experience  has  not  been  satisfactory  with  the 
continuous  plan,  and  it  is  for  this  reason  that  in  all  our  recent  plants, 
we  have  been  installing  the  intermittent  system.  Until  shown  to  the 
contrary,  we  think  that  this  offers  the  best  solution,  in  that  with  it  you 
have  complete  control  of  the  necessary  density  for  the  filters,  there  is 
no  danger  from  losses  in  the  overflow,  and  the  froth  which  accumu- 
lates during  the  filling  of  the  tank  is  completely  disposed  of  at  each 
cycle  of  the  operation,  and,  therefore,  cannot  accumulate.  The  agitator 
for  stirring  the  contents  of  the  tank  during  the  discharge  period  is 
copied  from  those  used  at  the  Goldfield  Consolidated  mill.  It  consists 
of  arms  secured  to  a  square  revolving  shaft,  suspended  by  a  chain- 
block,  and  passing  through  a  square  hole  in  the  driving-gear.  It  is 
simple,  inexpensive,  and  gives  no  trouble  whatever.  It  is  illustrated 
in  the  accompanying  figure.  The  thickened  pulp  may  be  drawn  off 
from  a  central-bottom  discharge.  More  recent  practice  is  to  draw  off 
through  a  valve  or  molasses  gate  on  the  side  of  the  tank,  or  better  still, 
with  a  diaphragm-pump."  Fig.  1  shows  an  installation  for  a  60-ton 
zinc  plant. 


DISPOSAL  OF  FLOTATION  PRODUCTS 


249 


250 


FLOTATION 


The  following  examples  illustrate  the  practice  of  filtering  flotation 
concentrate. 

1.  Montezuma  Mines  &  Milling  Co.,  Montezuma,  Colorado.     This 
plant  is  producing  daily  10  tons  of  concentrate  that  assays  42%  zinc 
and  9%  iron.    The  froth  is  sent  to  tables  and  the  table-concentrate  is 
filtered.    The  cake  contains  only  3%  moisture. 

2.  Portland  Gold  Mining  Co.,  Victor,  Colorado.    From  13  to  15 
tons  of  concentrate,  assaying  55  to  70%  silica  and  2  oz.  gold,  is  made 
daily.     The  froth  goes  to  Dorr  thickeners  and  Portland  filters.     The 
moisture  in  the  filter-cake  is  30%.    The  concentrate  is  loaded  by  hand 
into  tight-bottom  box-cars.     Cost  of  dewatering  and  loading  is  50c. 
per  ton.     The  results  are  not  considered  satisfactory. 

3.  Name  omitted.     Daily  production  is  10  tons  of  concentrate, 


FIG.    Ib.       PLAN   OF   AGITATORS    IN    MAGMA   MILL 

assaying  40%  zinc,  7%  silica,  14%  iron,  30%  sulphur,  7%  lead,  with 
a  little  gold,  silver,  and  copper.  This  is  dewatered  in  Portland  filters 
to  14%  moisture,  and  loaded  by  hand  into  unlined  box-cars.  The  cost 
for  dewatering  and  loading  is  15c.  per  ton. 

4.  St.  Joseph  Lead  Co.,  Bonne  Terre,  Missouri.     Forty  tons  of 
concentrate  is  handled  per  day.     The  analysis  is  50%  lead,  2%  zinc, 
9%  lime,  4%  iron,  and  6%  insoluble.      The  froth,  containing  90% 
moisture,  goes  to  a  38  by  6  ft.  Dorr  thickener,  which  gives  a  spigot- 
product  of  35%  moisture.    This  pulp  is  sent  to  one  11  ft.  6  in.  by  12  ft. 
Oliver  filter,  a*nd  the  cake,  containing  14%  moisture,  is  loaded  into 
gondola  cars  by  means  of  a  rubber-belt  conveyor.     A  Root  vacuum- 
pump,  requiring  29^  hp.  is  used  for  the  filter.     The  operation  of  the 
filter  itself  required  1£  hp.     Cost  for  dewatering  is  26c.,  for  loading 
2c.,  and  for  maintenance  6c.,  making  a  total  of  34c.  per  ton. 

5.  Engels  Copper  Mining  Co.,  Taylorsville,  California.    Between 
30  and  40  tons  of  concentrate  is  produced  in  16  hours.     The  assay  is 
35%  copper  and  30%  insoluble.    The  froth  is  elevated  to  two  settling- 
tanks  having  cone-shaped  bottoms.     The  thickened  concentrate  then 


DISPOSAL  OF  FLOTATION  PRODUCTS  251 

goes  to  an  8  by  8-ft.  Oliver  filter,  which  gives  a  cake  containing  12% 
moisture.  Steam  is  used  to  heat  the  pulp  in  the  filter-tank.  The  filter- 
product  is  sacked  and  carried  1 J  miles  by  a  tram  to  auto-trucks,  which, 
in  turn,  carry  the  concentrate  to  the  railroad  30  miles  away.  The  cost 
for  dewatering  and  filtering  is  $1.50  per  ton. 

6.  Bunker  Hill  &  Sullivan  Co.,  Kellogg,  Idaho.    Analysis  of  con- 
centrate is  45.9%  lead,  6.6%  zinc,  13.2%  sulphur,  10.4%  insoluble, 
9.8%  iron,  26.6  oz.  silver  with  a  little  copper  and  manganese.    Twenty 
tons  is  produced  per  day,  all  of  it  -  200  mesh.  A  40  by  12-ft.  Dorr  thick- 
ener and  a  6  by  8-ft.  Oliver  filter  are  used  for  dewatering.    The  filtered 
concentrate  contains  11%  moisture.     It  is  loaded  into  box-cars.     The 
cost  is  7c.  for  dewatering  and  15c.  for  loading,  making  a  total  of  22c. 
per  dry  ton.     It  is  essential  that  the  feed  to  the  filter  be  as  thick  as 
possible,  about  35%  moisture  being  a  satisfactory  figure.    It  has  been 
found  that  wiping  the  oily  film  that  forms  on  the  filter-cake,  with  a 
rawhide  beater,  reduces  the  moisture  nearly  one-half. 

7.  Detroit  Copper  Mining  Co.,  Morenci,  Arizona.     All  flotation 
concentrate  goes  to  one  Dorr  thickener.    A  6  by  8-ft.  Oliver  filter  takes 
as  much  of  the  thickened  product  as  it  can  handle,  together  with  the 
froth  from  the  top  of  the  thickener,  which  is  removed  by  paddle- 
wheels.     The  slime-overflow  from  the  thickener  is  sent  to  a  settling- 
tank,  and  the  spigot-product  is  shipped  as  flotation  slime.    An  analy- 
sis of  a  composite  sample  of  the  filter-product  and  slime  is  20.32% 
copper,  22.3%   silica,   13.2%   iron,   12.6%   alumina,   1.4%   lime,   1% 
magnesia,  and  19.8%  sulphur.     The  moisture  in  the  filtered  concen- 
trate is  34.6%,  and  the  slime  carries  80.6%  moisture,  which  necessi- 
tates its  being  shipped  in  tank-cars.     The  equipment  is  inadequate, 
and  a  larger  plant  is  required  to  give  satisfactory  results. 

8.  Consolidated     Nevada-Utah     Corporation,     Pioche,     Nevada. 
About  half  of  the  total  tonnage,  18  tons  of  concentrate  per  day,  is 
thickened  and  filtered.     It  assays  42%  zinc,  10%  iron,  1%  lead,  and 
11%  insoluble.     The  flotation  concentrate  is  very  slimy  and  is  mixed 
with  the  fine  concentrate  from  the  tables  in  order  to  obtain  a  product 
that  can  be  filtered  satisfactorily.     The  coarse  concentrate  from  the 
roughing-tables  is  not  filtered.     Three  16-ft.  agitators  are  used  for 
thickening.    One  is  running  and  one  is  filling  while  the  third  is  being 
decanted.    Each  requires  5  lip.    The  4  by  8-ft.  Portland  filter  reduces 
the  moisture  to  between  9  and  10%  and  consumes  1  hp.  for  operation. 
The  concentrate  is  shipped  in  box-cars  with  a  12-in.  board  nailed  across 
the  door. 

9.  Old  Dominion  Copper  Mining  &  Smelting  Co.,  Globe,  Arizona. 


252  FLOTATION" 

Of  the  36  dry  tons  of  concentrate  handled  per  day,  fully  91%  is  -  200 
mesh.  An  analysis  gives  18%  copper,  24%  iron,  27%  sulphur,  and 
22%  insoluble.  The  froth,  containing  8%  solid,  is  pumped  by  a  3-in. 
centrifugal  pump  to  a  10  by  28-ft.  Dorr  thickener,  which  gives  a 
spigot-product  of  about  57%  solid.  This  goes  to  an  8  by  11.5-ft.  Oli- 
ver filter.  The  filter-cake  contains  19%  moisture.  The  filter  dis- 
charges into  a  bin  from  which  the  concentrate  is  loaded  into  cars  by 
means  of  wheelbarrows.  The  power  consumption  of  thickener  and 
filter  is  1.24  kw.  per  hour.  The  filter  operates  at  a  21-in.  vacuum  and 
18  Ib.  for  blowing-pressure.  Cost  is  1.6c.  for  dewatering  and  filter 
power,  8c.  for  repairs  to  filter  and  renewal  of  canvas,  and  21c.  for 
loading  concentrate,  making  a  total  of  30. 6c.  per  ton.  The  compara- 
tively high  cost  of  loading  is  due  to  the  necessity  of  loading  into  box- 
cars, which  makes  it  impossible  to  use  a  belt-conveyor.  Trouble  is 
experienced  from  the  accumulation  of  froth  in  the  thickener.  This 
robs  the  thickener  of  settling  and  thickening  capacity.  Sprays  of 
water  break  up  some  of  the  froth  but  do  not  prevent  a  gradual  ac- 
cumulation. 

10.  Utah  Leasing  Co.,  Newhouse,  Utah.     The  froth  goes  to  a  22 
by  10-ft.  Dorr  thickener  and  then  to  an  8  by  6-ft.  Oliver  filter,  which 
gives  a  product  containing  20  to  21%  moisture.     Great  difficulty  is 
experienced  in  settling  and  filtering  the  fine  slime.     Sodium  silicate, 
soda-ash,  and  lime  have  been  tried,  but  without  marked  success.     Al- 
lowing 24  hours,  or  more,  of  undisturbed  settling  in  tanks  seemed  to 
be  of  little  avail.     Fifteen  tons  of  concentrate  is  produced  daily.     It 
assays  15  to  16%  copper,  33  to  36%  silica,  and  20  to  22%  iron. 

11.  Gold   Hunter  Mining  &   Smelting   Co.,   Mullan,    Idaho.      A 
screen-analysis  of  the  30  tons  of  concentrate  produced  per  day  shows 
the  following  results:   +  100  mesh,  0.2%  ;  -f  150  mesh,  1.8%  ;  +  200 
mesh,  6.4%;  and  -200  mesh,  91.6%.     It  is  a  lead  concentrate  with 
about  16%  silica.     The  froth  is  thickened  to  more  than  50%  solid 
in  a  30  by  5-ft.  Dorr  thickener.    Froth,  running  60%  solid,  is  mechan- 
ically skimmed  at  the  top  of  the  tank  and  unites  with  the  spigot-prod- 
uct, going  to  an  8  by  6-ft.  Oliver  filter.    A  vacuum  of  from  24  to  25 
in.  is  maintained  by  a  wet-vacuum  pump.     A  receiver  with  a  baro- 
metric leg  is  used  for  the  filtrate,  which  is  clean  but  is  run  to  settling- 
tanks.     Oakdale  No.  3  twill  is  used  for  the  filter-cover.     It  lasts  six 
months.    The  agitator  is  run  at  30  r.p.m.,  but  the  air-lifts  are  not  used. 
The  emergency  air-agitators  are  used  once  daily.    The  canvas  is  blown 
from  one  to  three  times  per  day  with  compressed  air  under  20  Ib. 
pressure.     Occasionally  the  canvas  is  steamed,  using  a  1-in.  pipe  per- 


DISPOSAL  OF  FLOTATION  PRODUCTS  253 

forated  every  inch  with  yV-in.  holes.  Steam-pressure  is  60  Ib.  per 
square  inch.  A  scraper  is  mounted  on  a  flat  rigid  casting  that  holds 
it  just  off  the  wires.  The  dried  product  drops  into  a  bin,  from  which 
it  is  loaded  into  unlined  box-cars  by  means  of  wheelbarrows.  The 
concentrate  contains  10%  moisture.  The  overflow  from  the  thickener 
is  generally  clean,  but,  at  times,  a  little  froth  escapes.  The  overflow 
goes  to  settling-tanks  and  ponds.  The  cost  is  4Jc.  for  dewatering,  of 
which  3  jc.  is  for  power  and  the  rest  is  for  repairs  and  labor.  Loading 
costs  14c.  per  ton,  being  based  on  a  wage  of  $4.50  for  8  hours.  The 
filtered  concentrate  takes  up  more  space  and  this  adds  to  the  cost,  as  it 
has  to  be  shoveled  back  into  cars. 

12.  Anaconda  Copper  Mining  Co.,  Anaconda,  Montana.     From 
1800  to  1900  tons  of  wet  concentrate  is  produced  per  day.     This  is 
about  148  tons  per  filter-day.    The  screen  analysis  shows :   +  48  mesh, 
0.19%  ;  -  48  and  +  200  mesh,  29.7%  ;  -  200  and  +  300  mesh,  11.91%  ; 
-300  mesh,  57.18%.     The  chemical  analysis  shows  9%  copper,  28% 
silica,  25%  iron  oxide,  10%  alumina,  and  27%  sulphur.     Twenty-one 
50  by  12-ft.  Dorr  thickeners  are  used.     The  thickeners  for  the  slime- 
concentrate  require  15  minutes  for  a  revolution  and  consume  0.6  hp. 
each.     Those  for  the  sand-concentrate  revolve  once  in  9  minutes  and 
consume  1.5  hp.  each.    The  thirteen  11J  by  12-ft.  Oliver  filters  require 
1  hp.  each  for  operation,  25  hp.  each  for  wet  vacuum,  and  15  hp.  each 
for  dry  vacuum.     The  filter-feed  is  thickened  to  50%  solid  and  the 
cake  runs  15%  moisture.    The  pulp  is  heated  to  100°  F.  in  the  filter- 
tank.     The  filtered  concentrate  is  taken  directly  to  the  roasters  on  an 
18-in.  belt-conveyor,  which  requires  25  hp.  for  its  operation.     The 
method  is  satisfactory.     The  belt-conveyor  handles  the  material  with- 
out difficulty .     The  froth,  containing  from  18  to  20%  solid,  is  deliv- 
ered to  a  baffle-box  at  the  centre  of  each  Dorr  thickener.     The  box  is 
about  5  ft.  square  and  extends  down  to  within  a  few  inches  of  the 
rakes.     Surrounding  this  is  another  baffle  about  15  ft.  square  and 
extending  about  18  in.  below  the  surface  of  the  water.     The  baffles 
catch  a  large  part  of  the  froth,  which  is  there  broken  up  by  a  spray  of 
water.    The  overflow,  containing  a  small  amount  of  fine  material  that 
will  not  settle,  is  run  to  a  slime-pond. 

13.  Calaveras  Copper  Co.,  Copperopolis,   California3.     The  con- 
centrate contains  14.4%   copper,  29.5%   iron,  and  14.9%   insoluble. 
When  the  remodeling  of  the  plant  is  completed  about  50  tons  of  con- 
centrate will  be  produced  daily.     At  present  the  output  is  25  to  28 


3H.  R.  Robbins,  M.  &  S.  P.,  November  25,  1916. 


254  FLOTATION 

tons.  The  froth  is  thickened  to  60%  solid  in  a  22  by  10-ft.  Dorr  thick- 
ener and  the  moisture  is  reduced  to  13%  by  means  of  an  8-ft.  Oliver 
filter.  In  the  new  plant,  it  is  planned  to  convey  the  thickened  product 
to  the  niters  through  a  5-in.  pipe,  which  will  contain  a  1-in.  steam-pipe. 
This  will  heat  the  pulp  without  diluting  it  with  the  condensed  steam. 

14.  Braden  Copper  Co.,  Chile.    Both  the  table  and  flotation  con- 
centrates are  run  into  concrete  settling-tanks  at  the  bottom  of  the  mill. 
There  are  eight  tanks  in  all,  and  four  are  used  together  alternately. 
The  settled-table  and  coarse-flotation  concentrates  are  loaded  by  a  grab- 
bucket  into  cars.     The  tank-overflow,  having  a  water-ratio  of  10  or 
20 : 1,  goes  to  Dorr  thickeners  and  the  thickened  product  (water-ratio 
of  1 : 1),  is  sent  to  two  Kelly  and  four  Oliver  niters,  only  four  of  which 
are  in  operation  at  the  same  time.    About  50  tons  of  solid  per  day  is 
recovered  in  this  manner.    The  fineness  of  the  material,  98%  of  which 
is  -200  mesh,  results  in  low  filter-capacity.     At  this  plant  supplies 
constitute  60.4%  of  the  total  direct  milling-cost.  Concentrate-handling 
makes  up  8.33%  of  the  total  labor  and  1.14%  of  the  total  supplies. 
Filtering  concentrate  makes  up  5.46%  of  the  total  labor  and  2.61% 
of  the  total  supplies.     About  50  tons  is  handled  per  day,  of  which 
98%  is -200  mesh. 

15.  Inspiration  Consolidated  Copper  Co.,  Miami,  Arizona.     Five 
60-ft.  and  three  80-ft.  Dorr  thickeners  are  used  for  handling  651  dry 
tons  per  day  of  mixed  table  and  flotation  concentrates.     The  latter 
amounts  to  75%  of  total  concentrates  by  weight  and  carries  90%  of 
the  copper.    This  gives  44.8  sq.  ft.  settling-area  per  ton  of  concentrate. 
The  thickened  product,  having  a  water  ratio  of  1.65 : 1,  passes  through 
tunnels  to  two  bucket-elevators,  which  deliver  it  to  six  11  ft.  6  in.  by 
12-ft.    Oliver   filters.      The   filter-cake   contains   approximately    17% 
moisture.    In  attempting  to  reduce  the  moisture  in  the  cake,  the  pulp 
in  the  filter-tanks  was  heated  by  steam.     This  increased  the  capacity 
of  the  filters,  but  did  not  affect  the  moisture  in  the  cake.     Adding 
slaked  lime  gave  the  same  result.     Lime  is  now  used  to  increase  the 
capacity  of  the  filters.    A  double  ring  of  high  boards  is  used  to  pre- 
vent the  contamination  of  the  thickener-overflow  by  the  froth  accum- 
ulated on  top.    A  record  was  kept  of  the  portion  of  silica  in  the  con- 
centrate and  the  moisture  in  the  filter-cake.     The  results  are  shown  in 
the  accompanying  chart,  Fig.  2  (Sept.  1916  Bull.,  A.  I.  M.  E.),  and 
would  seem  to  indicate  that  the  amount  of-  moisture  remaining  in  the 
cake  depends  upon  the  silica  present  in  the  concentrate.     An  18-in. 
belt-conveyor  running  at  a  speed  of  150  ft.  per  min.  carries  the  con- 
centrate to  a  steel  loading-bin,  directly  above  the  railroad  track.     At 


DISPOSAL  OF  FLOTATION  PEODUCTS 


255 


the  head  pulley  a  rubber  scraper  is  used  to  assist  in  removing  the  con- 
centrate from  the  belt-conveyor.  The  bin  is  round  with  a  cone-shaped 
bottom.  Some  difficulty  is  experienced  in  discharging  the  material 
from  the  bin.  The  total  power-consumption  for  thickening,  elevating, 
filtering,  and  conveying  is  5.1  kw-hr.  per  ton  of  concentrate.  The  cost 
of  dewatering  and  loading  is  between  20  and  25c.  per  ton. 

A  certain  plant,  producing  15  tons  of  a  12%  copper  concentrate 
per  day,  uses  a  Dorr  thickener  and  a  4  by  8-ft.  Oliver  filter.  The  cake 
is  shoveled  into  wagons.  Cost  for  dewatering  and  loading  is  given  as 
50c.  per  ton.  Another  plant,  making  35  tons  of  zinc-lead  concentrate 
per  day,  delivers  the  froth  to  a  bucket-elevator  in  order  to  break  it  up. 


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FlG.   2.      CHART  SHOWING  SILICA  IN  CONCENTRATE  AND  MOISTURE  IN  FILTER-CAKE 


It  then  goes,  without  dewatering,  to  an  Oliver  filter,  which  gives  a  cake 
containing  10%  moisture.  This  is  loaded  into  gondola  cars  lined  with 
canvas.  The  cost  is  lOc.  per  ton. 

A  copper  company,  which  produces  from  15  to  18  tons  of  concen- 
trate per  day,  assaying  from  14  to  18%  copper  and  28  to  34%  silica, 
thickens  the  froth  in  Callow  cones  and  then  sends  it  to  an  Oliver  filter. 
The  filter-cake  drops  down  a  chute  lined  with  1.5-in.  steam-pipes  into 
a  bin,  which  is  also  lined  with  steam-pipes.  The  concentrate  is  then 
shoveled  from  the  bin,  and  shipped  in  gondola  cars  patched  with  sacks 
and  thin  boards.  In  spite  of  the  filtering  and  drying,  the  shipping- 
concentrate  runs  from  14  to  18%  moisture.  It  is  so  wet  and  sticky 
that  it  requires  a  great  deal  of  shoveling.  Cost  of  loading  is  from  22 
to  25c.  per  ton.  The  dewatering  and  drying  cost  is  not  known. 

SMELTING  FLOTATION  CONCENTRATE.     The  concentrate  generally 


256 


FLOTATION 


comes  to  smelters  so  well  established  in  methods  of  operation  that  their 
work  is  of  a  routine  nature.  If  this  material  is  put  through  the  reg- 
ular smelting  process,  it  has  been  found  that  the  physical  condition  of 
the  concentrate  is  such  as  to  require  certain  modifications  in  the  usual 
methods  of  operation. 

The  actual  smelting  of  a  flotation  product  is  quite  similar  to  the 
smelting  of  any  other  concentrate.  The  objections  to  it  are  of  a  phys- 
ical rather  than  of  a  chemical  nature,  but  they  are  enough  to  cause 
many  smelters  to  impose  a  penalty  of  $1  per  ton.  If  the  concentrate 


FIG.  3. 


LUMPS    OF    INCOMPLETELY    ROASTED    ZINC    CONCENTRATE    SHOWING 
UNALTERED    CORES    OF    SULPHIDE 


arrives  at  the  smelter  in  a  wet  and  sticky  condition,  it  is  difficult  and 
expensive  to  unload.  A  large  moisture-content  means  extra  fuel- 
consumption  in  driers  and  roasters,  and  in  furnaces,  when  charged 
directly  into  them.  The  great  fineness  of  the  material  causes  a  heavy 
loss  from  dusting.  This  is  especially  true  where  it  is  necessary  to 
smelt  in  blast-furnaces.  Briquetting  should  reduce  this  loss,  but  it  is 
often  difficult  to  produce  satisfactory  briquettes,  Unless  it  can  be 
mixed  with  a  large  proportion  of  coarse  material,  flotation  concentrate 
is  hard  to  sinter.  It  chokes  the  grates,  interferes  with  the  draft,  and 
reduces  the  capacity  of  the  sintering  machines.  In  some  cases  it  may 
be  necessary  to  pre-roast  before  a  successful  sinter  can  be  produced. 
During  the  roasting  process,  there  is  often  a  marked  tendency  toward 
agglomeration  or  'balling  up,'  and  lumps  are  formed  that  roast  on  the 
outside  only.  Fig.  3  shows  two  lumps  (natural  size)  of  zinc  concen- 
trate that  passed  through  the  roaster,  but  came  out  with  unaltered 
cores.  Often  troublesome  accretions  are  formed  in  the  roasters.  At 
one  plant  it  was  found  that  a  preliminary  drying  of  the  concentrate 
before  roasting  prevented  'balling.'  However,  drying  usually  makes 


DISPOSAL  OF  FLOTATION  PRODUCTS  257 

the  material  lumpy  and  hard  to  feed.  Where  a  large  amount  of  flota- 
tion concentrate  is  roasted,  special  apron-feeders  must  be  provided  to 
handle  this  material. 

The  roasted  product  is  of  such  a  light  and  fluffy  nature  that  it  must 
be  handled  with  great  care  to  keep  down  the  loss  from  dusting.  At 
one  plant,  the  cars  are  loaded  in  a  tunnel  connected  to  a  dust-chamber 
and  stack.  Should  a  sufficiently  large  amount  of  dust  be  produced,  it 
would  pay  to  add  a  Cottrell  tube-system.  At  another  copper  smelter, 
the  side  walls  of  the  reverberatory  furnaces  have  slots  cut  through 
them  just  above  the  slag-line.  Inclined  iron  plates  are  fastened  to  the 
outside  of  the  walls  so  that  the  charge  can  be  shoveled  onto  them  and 
work  slowly  down  into  the  furnace  as  the  smelting  proceeds.  This 
method  of  gently  presenting  the  charge  to  the  heat  at  a  point  where  the 
draft  is  weakest  causes  a  minimum  formation  of  dust.  It  is  far  less 
than  if  centre-charging  is  used. 

The  foregoing  discussion  concerns  lead  and  copper  smelting,  but 
zinc  smelters,  as  well,  have  their  troubles  when  treating  flotation  con- 
centrate. At  one  plant,  the  unloading  from  cars  is  done  by  shoveling 
or  by  a  grab-bucket.  The  material  is  then  dried  in  a  rotary  drier  and 
roasted  in  muffle-kilns.  Because  of  its  fineness,  it  is  considered  more 
difficult  to  treat  than  other  zinc  concentrate.  At  a  second  plant,  all 
the  unloading  is  done  by  shoveling,  but  it  is  considered  an  unsatisfac- 
tory method.  At  a  third  plant,  shoveling  is  considered  expensive, 
though  it  is  acceptable  in  other  regards.  The  concentrate  is  roasted 
in  open-hearth  furnaces  fired  with  natural  gas.  Very  little  trouble  is 
experienced  in  roasting.  No  difficulty  is  found  in  smelting,  but  the 
dust-loss  is  higher  than  for  coarser  material.  At  a  fourth  plant,  flota- 
tion concentrate  makes  trouble  all  through  the  smelting  process.  Un- 
loading is  done  by  shoveling  into  wheelbarrows.  The  material  is 
frozen  in  winter  and  is  hard  to  handle.  It  is  roasted  in  reverberatory 
furnaces  to  1%  sulphur  or  less  (cost  of  roasting  is  about  $1.70  per 
ton).  The  coarse  concentrate  is  first  dried  to  about  4%  moisture,  but 
the  fine  concentrate  is  not  dried.  The  difficulties  found  in  roasting  are 
high  dust-loss,  the  forming  of  accretions  in  the  roasters,  and  the  fusing 
of  the  fine  concentrate.  Smelting  is  done  in  the  usual  gas-fired  dis- 
tillation-furnaces. The  fine  material  is  more  subject  to  loss  through 
overheating.  It  slags  more  easily  with  consequent  loss  of  retorts.  The 
charge  is  more  likely  to  cake  in  the  charge-cars,  if  too  wet,  and  to  blow 
out  of  the  retorts,  if  too  dry.  The  very  fine  flotation  concentrate  is 
difficult  to  roast  and  smelt. 

One  smelter  superintendent  forcibly  summarizes  the  situation  in 


258  FLOTATION 

the  following  brief  sentence.     "Flotation  concentrate  is  considered  a 
damned  nuisance." 

Examples  of  smelting  practice  are  given  below. 

1.  Consolidated  Mining  &  Smelting  Co.  of  Canada,  Trail,  B.  C. 
The  amount  of  flotation  concentrate  smelted  is  too  small  to  afford  reli- 
able data.    It  is  charged  directly  into  blast-furnaces,  so  that  the  dust- 
loss  probably  is  serious.    A  briquetting  plant  is  being  installed. 

2.  Omaha  Plant,  American  Smelting  &  Refining  Co.,  Nebraska. 
The  copper  concentrate,  used  incidentally  to  supply  sulphur  to  the 
charge,  is  briquetted  with  1%  lime,  and,  after  drying  for  72  hours,  is 
charged  into  the  blast-furnaces.    This  material,  even  after  briquetting, 
produces  considerable  flue-dust. 

3.  U.  S.  Smelting  Co.,  Midvale,  Utah.     The  concentrate  is  shov- 
eled from  the  cars  and  is  briquetted  with  flue  or  bag-house  dust,  heavy 
with  lime  that  had  been  introduced  for  the  purpose  of  neutralization. 
The  cost  is  about  $1  per  ton.    The  sintering  in  Dwight-Lloyd  machines 
is  not  good,  due  to  a  poor  mixing.     The  product  is  smelted  in  lead 
blast-furnaces.    Flotation  concentrate  is  considered  a  great  nuisance. 

4.  Garfield  Smelting  Co.,  Garfield,  Utah.     The  flotation  concen- 
trate is  mixed  with  table  and  vanner  products.    It  is  then  bedded  with 
fluxing  ores  and  later  fed   to  McDougall   and   Herreshoff   roasters. 
While  the  quantity  of  flotation  concentrate  treated  is  too  small  to  cause 
any  serious  difficulty  or  to  require  special  treatment,  close  observation 
shows  that  it  has  a  tendency  to  form  lumps  that  do  not  break  up  easily 
in  the  roasters.    In  fact,  some  lumps  roast  only  on  the  outside.    A  large 
increase  in  the  amount  of  flotation  concentrate  handled  would  prob- 
ably necessitate  a  special  feeding  device. 

5.  Selby  Smelting  Co.,  California.     The  flotation  concentrate  is 
unloaded  by  shoveling  and  is  spread  out  to  dry.     Cost  for  spreading 
is  about  30c.  per  ton.     It  is  then  sintered  and  smelted  in  lead  blast- 
furnaces.    No  trouble  is  experienced,  other  than  the  production  of  a 
large  amount  of  flue-dust. 

6.  Anaconda  Copper  Mining  Co.,  Montana.     About  20%  of  fine 
table  and  jig  concentrate  is  mixed  with  the  flotation  product.    This  is 
delivered   to  Wedge   roasters  by   belt-conveyors.      Each   furnace-bin 
holds  25  tons.     A  large  steel  apron-feeder  is  used  for  supplying  the 
material  to  the  furnace.     The  roasted  product  is  extremely  fine  and 
difficult  to  handle.    It  is  loaded  into  covered  cars  in  a  tunnel  that  is 
entirely  closed  except  for  a  stack  at  one  end,  which  produces  a  slight 
draft.     The  amount  of  dust  issuing  from  the  stack  is  small.     If  suffi- 
ciently valuable,  the  dust  could  be  recovered  by  a  Cottrell  precipitator. 


DISPOSAL  OF  FLOTATION  PRODUCTS  259 

The  smelting  in  coal-fired  reverberatory  furnaces  presents  no  diffi- 
culties. 

7.  Murray  Plant,  American  Smelting  &  Refining  Co.,  Utah.  The 
flotation  concentrate  arriving  at  this  plant  is  wet  and  sticky,  and  bad 
to  handle.  It  is  mixed  with  sulphide  ores  and  roasted  or  sintered  and 
then  smelted  in  lead  blast-furnaces.  It  is  considered  to  have  an  ad- 
verse effect  on  the  smelting  process.  It  chokes  the  roasters  and  tends 
to  give  a  poorly-roasted  product.  The  dust-loss  is  heavy.  The  fine 
powdery  product  is  objectionable  from  a  lead-smelting  standpoint. 

8.  Ohio  &  Colorado  Smelting  &  Refining  Co.     All  flotation  con- 
centrate is  either  pre-roasted  and  sintered  or  sintered  directly.     The 
pre-roasting  is  done,  after  mixing  with  coarser  material,  in  Godfrey 
and  Wedge  furnaces.     The  flue-dust  and  mechanical  dust-loss  is  in- 
creased.   Dwight-Lloyd  machines  are  used  for  sintering.    Even  though 
coarser  material  is  added,  the  capacity  of  the  sintering-machines  is 
decreased. 

9.  Bartlesville  Zinc  Co.,  Bartlesville,  Oklahoma.     The  zinc  con- 
centrate from  filter-presses  is  unloaded  by  shoveling.    It  must  be  dried 
in  a  machine  of  special  design  to  avoid  excessive  dust-loss.    It  is  then 
roasted  in  ordinary  kilns.     Allowance  for  excessive  dust-losses  met 
with  at  every  step  in  its  treatment  should  be  provided  for  when  pur- 
chasing flotation  concentrate. 

10.  Braden  Copper  Co.,  Chile.4     The  first  flotation  concentrate 
produced  at  the  plant  was  so  wet  that  it  could  not  be  briquetted,  and 
so  fine  that  it  was  hard  to  filter  and  dry.    When  charged  directly  into 
the  blast-furnaces,  the  amount  of  coke  required  was  increased  from  12 
to  16%.    The  drained  concentrate  from  the  bins  contained  50%  mois- 
ture and  the  filtered  concentrate  ran  30%   moisture.     After  much 
experimenting,  it  was  found  that  nodulizing  in  rotating  kilns  gave  a 
product  that  was  a  first-class  smelting  material. 

11.  International  Smelting  Co.,  Miami,  Arizona.    The  concentrate 
is  unloaded  from  steel  cars,  having  removable   bottoms,   onto  belt- 
conveyors  that  deliver  it  to  bedding-bins,  where  the  necessary  fluxes 
are  added.     The  beds  contain  about  4000  tons,  80%  of  which  is  flota- 
tion concentrate,  and  are  made  in  V-shaped  steel  bins  that  have  remov- 
able-slat bottoms.    Beginning  at  one  end,  the  mixture  is  fed  from  an 
approximately  vertical  face  onto  a  belt-conveyor,  which  discharges 
into  Wedge  roasters,  used  as  driers  only.     The  material  is  sticky  and 
hard  to  handle.    It  is  dried  to  about  14%  moisture,  and  is  then  fed  to 


4R.  E.  Douglass  and  B.  T.  Colley,  Eng.  <f-  Min.  Jour.,  February  12,  1916. 


260  FLOTATION 

oil-fired  reverberatory  furnaces.  The  difficulties  in  smelting  are  prac- 
tically of  a  mechanical  nature,  due  to  the  handling  of  this  extremely 
fine  charge,  50%  of  which  is  -200  mesh.  The  plant  was  designed  for 
smelting  flotation  concentrate,  and  every  precaution  was  taken  to 
avoid  dust-losses. 

12.  At  Mt.  Morgan,   Queensland,  Australia,5  an  ore  containing 
about  2%  copper  and  from  $5  to  $7  in  gold  is  treated  by  flotation. 
Nearly  70%  of  the  gold  is  free.    It  was  found  that  by  grinding  the  ore 
very  fine,  much  of  the  gold  was  caught  in  the  thick  froth  of  the  flota- 
tion-machine.   The  ore  was  ground  to  80-mesh.    There  was  no  increase 
in  the  saving  of  copper,  but  the  extra  gold  recovered  paid  for  the  cost 
of  grinding.    As  long  as  only  a  small  tonnage  was  treated,  the  concen- 
trate was  mixed  with  blast-furnace  flue-dust,   in  the  proportion  of 
1 :  3,  and  sintered  in  a  Dwight-Lloyd  machine  with  excellent  results. 
But  when  the  percentage  of  concentrate  was  increased,  the  sulphur 
content  rose  to  such  a  figure  that  the  machine  did  not  give  a  good 
product,  and  its  capacity  was  reduced,  owing  to  the  choking  of  the  bed 
by  fine  concentrate.     Pre-roasting  followed  by  pot-roasting  was  then 
tried.     An  Edwards  furnace  was  first  used,  but  the  roasted  product 
was  so  fine  that  it  could  not  be  handled  in  the  Dwight-Lloyd  machine 
or  in  the  pots.    Tests  made  by  pre-roasting  in  a  Godfrey  furnace  and 
sintering  in  pots  proved  satisfactory,  and  such  a  plant  was  installed. 
It  was  found  that  the  product  from  the  Godfrey  furnace  was  coarser 
than  the  concentrate,  some  agglomeration  evidently  taking  place.     A 
sketch  of  one  of  the  sintering-pots  is  shown  in  the  accompanying  figure. 

13.  Tacoma  Smelting  Co.,  Tacoma,  Washington.     The  flotation- 
concentrate  arriving  at  this  plant  is  unloaded  from  ships  in  tubs  that 
are  filled  by  hand-shoveling.     Owing  to  the  sticky  character  of  the 
material,  this  work  is  disagreeable  and  costly.     Roasting  is  done  in 
Herreshoff  furnaces,  the  upper  floors  of  which  are  used  for  drying 
only.    It  is  necessary  to  clean  the  roasters  frequently.     Reverberatory 
furnaces  are  used  for  smelting.     Elaborate  machinery  must  be  used 
in  order  to  keep  dust-losses  from  becoming  excessive. 

14.  Helena  (Montana)  plant  of  A.  S.  &  R.  Co.     Unless  filtering 
or  drying  has  been  done  at  the  mill,  the  flotation-concentrate  sent  to 
this  plant  carries  from  20  to  25%  moisture.    In  summer  this  material 
has  the  consistence  of  liquid  mud,  and  could  almost  be  unloaded  from 
cars  by  means  of  a  pump.    In  practice,  men  wearing  high  rubber  boots 
shovel  the  concentrate  from  the  cars  into  bins.    The  cars  can  be  washed 


r-B.  Magnus,  'Sintering  Flotation  Concentrates.'     Eny.  d-  Min.  Jour..  June 
10,  1916. 


DISPOSAL  OF  FLOTATION  PRODUCTS 


261 


262  FLOTATION 

out,  but  the  material  sticks  to  the  sides  of  the  bins,  dries,  and  causes 
loss  from  dusting.  In  winter  the  concentrate  will  freeze  solid  in  the 
car,  and  has  to  be  thawed  or  else  mined  with  gads  and  picks.  The  cost 
of  unloading  is  then  excessive.  No  particular  difficulty  is  presented 
when  the  concentrate  has  been  dried  or  filtered  before  shipping.  The 
lead  concentrate  is  first  sintered  in  Dwight-Lloyd  machines.  From 
10  to  15%  of  flotation-concentrate  is  mixed  with  miscellaneous  sulphide 
ores,  including  a  small  quantity  of  matte  and  from  5  to  10%  of  crushed 
limestone.  With  this  mixture  a  fairly  good  sinter  can  be  obtained. 
This  material  is  then  transferred  to  H.  &  H.  pots,  where  it  is  converted 
into  a  slagged  and  fairly  porous  product  containing  less  than  2% 
sulphur.  .  Smelting  in  lead  blast-furnaces  presents  no  difficulties. 
Owing  to  its  extreme  fineness,  smelters  must  necessarily  suffer  consid- 
erable loss  from  dusting  when  handling  flotation-concentrate.  This 
loss  is  undoubtedly  higher  than  in  the  case  of  ordinary  ores  or  coarse 
concentrate ;  therefore  it  justifies  a  higher  charge  for  treatment. 

SUMMARY.  The  various  methods  of  handling  froth  may  be  classi- 
fied as  follows : 

1.  Breaking  by  means  of  centrifugal  pumps,   bucket-elevators, 
jets,  or  on  tables. 

2.  Dewatering  in  tanks,  with  or  without  filter-bottoms.     Steam 
may  be  used  to  assist  drying. 

3.  Dewatering  in  classifiers  of  the  Ovoca  and  Akins  type. 

4.  Continuous  thickening,  followed  by  filtering. 

5.  Intermittent  thickening,  followed  by  filtering. 

The  use  of  tanks  for  dewatering  concentrate  necessitates  unloading 
by  shoveling,  unless  the  tonnage  to  be  handled  is  sufficiently  great  to 
warrant  the  installation  of  a  crane  and  grab-bucket.  The  cost  of  load- 
ing varies  from  lOc.  per  ton,  where  the  concentrate  can  be  shoveled 
directly  into  cars,  to  25c.  and  more  per  ton,  when  wheelbarrows  must 
be  used.  In  case  gondola  cars  are  to  be  loaded,  a  belt-conveyor  will 
reduce  the  cost  to  2  or  3c.  per  ton.  The  employment  of  steam  for  dry- 
ing can  hardly  be  recommended,  especially  where  pipes  are  placed  in 
tanks.  The  concentrate  should  be  spread  out  in  a  thin  layer  on  a 
uniformly  heated  surface.  In  a  tank  the  concentrate  in  contact  with 
the  steam-pipes  is  quickly  dried,  but  the  moisture  is  driven  out  only 
to  condense  in  the  main  body  of  the  concentrate,  which  dries  very 
slowly.  Such  a  method  of  dewatering  is  necessarily  expensive.  Filter- 
bottoms  for  tanks  may  be  advisable  where  the  concentrate  drains  fairly 
well,  and,  in  such  instances,  the  trouble  from  accumulated  froth  is 
eliminated.  Where  the  water  must  be  decanted  from  settled  concen- 


DISPOSAL  OF  FLOTATION  PRODUCTS  263 

trate,  the  decanting  apparatus  should  be  so  designed  that  it  can  work 
in  the  clear  water  between  the  unbroken  floating  froth  and  the  top  of 
the  settled  concentrate. 

Continuous  thickening,  followed  by  filtering,  is  a  method  commonly 
employed,  but  the  troubles  arising  from  the  accumulation  of  floating 
froth  in  the  thickener  and  the  difficulty,  at  times  experienced,  in  get- 
ting a  spigot  product  low  enough  in  moisture  for  satisfactory  filtering 
should  be  considered  when  making  such  an  installation.  One  large 
company  gives  the  cost  of  thickening  in  Dorr  thickeners,  dewatering 
on  a  continuous  filter  and  loading  by  gravity  at  65c.  per  ton.  Another 
company  states  that  thickening  and  filtering  (continuous  type)  costs 
lOc.  per  ton.  Intermittent  thickening,  followed  by  filtering,  seems  to 
offer  the  most  positive  control  over  the  moisture  in  flotation  concen- 
trate. Filters  of  the  pressure  type  will  give  good  results  on  material 
that  cannot  be  satisfactorily  treated  on  vacuum-filters. 

A  preliminary  treatment,  before  smelting,  is  nearly  always  given 
flotation  concentrate.  Such  treatment  would  come  under  one  of  the 
following  heads,  although  two  or  more  may  be  combined : 

1.  Drying. 

2.  Briquetting. 

3.  Nodulizing. 

4.  Sintering. 

5.  Roasting. 

The  difficulties  in  the  smelting  of  flotation  concentrate  are  caused 
by  the  extreme  fineness  of  this  material.  Briquetting  should  be  a  good 
method  of  preparing  the  concentrate  for  direct  smelting  in  blast- 
furnaces, but  it  is  not  easy  to  make  a  strong  briquette  that  will  not 
break  up  and  produce  much  flue-dust  before  it  is  smelted.  Nodulizing 
gives  an  excellent  smelting  product,  besides  driving  off  some  sulphur, 
but  the  loss  in  dust  may  be  considerable.  Roasting  presents  such 
troubles  as  the  necessity  of  specially  designed  feeders  for  furnaces, 
the  formation  of  accretions,  and  the  non-roasting  of  the  interior  of 
lumps,  heavy  dust-losses,  and  the  production  of  a  light  fluffy  product 
that  is  not  easy  to  handle.  The  cake  from  sintering  or  pre-roasting 
and  sintering  is  quite  suitable  for  feeding  to  blast-furnaces,  but  it  is 
necessary  to  mix  coarse  material  with  the  flotation  concentrate  in  order 
to  get  a  well-sintered  product  and  to  prevent  too  great  a  falling  off  in 
the  capacity  of  the  machines. 

At  the  present  time  flotation  concentrate,  being  a  new  and  unusual 
material,  is  difficult  to  handle.  Unless  specially  designed  for  the  pur- 
pose, smelters  cannot  be  expected  to  treat  this  product  in  the  smooth 


264  FLOTATION 

manner  of  their  ? regular  work.  However,  metallurgists  are  keenly 
interested  in  solving  the  problems  thus  presented,  and,  as  the  tonnage 
of  ores  that  are  being  concentrated  by  the  flotation  process  increases, 
plants  smelting  only  such  concentrate  will  soon  experience  no  serious 
hindrance  to  satisfactory  operation. 


SUMMARY  OF  RESULTS  WHEN  TREATING  SLIME  AT  ANACONDA 

1.  The  economic  capacity  of  the  M.  S.  No.  1  machine  when  treat- 
ing slime,  as  produced  from  the  mill  at  present,  is  approximately  80 
tons  per  24  hours.     We  have  found  that  the  tonnage  treated  by  the 
experimental  machine,  which  had  agitator  boxes  2  ft.  square,  is  to  that 
treated  by  the  full-size  machine,  with  boxes  3  ft.  square,  as  the  cross- 
sectional  area. 

2.  The  best  combination  of  reagents  for  the  treatment  of  slime 
seems  to  be  sulphuric  acid,  kerosene  acid-sludge,  wood-creosote,  and 
stove-oil.    There  is  some  question  as  to  the  real  value  of  stove-oil — its 
principal  function  being  to  make  a  more  compact  froth. 

3.  It  would  not  be  economical  to  retain  the  round  tables,  as  the 
recovery  by  treating  the  slime  directly  by  flotation  is  just  as  high  as 
by  retaining  the  round  tables  and  treating  the  round-table  tailing  by 
flotation.     The  heating  of  the  round-table  tailing  pulp,  on  account  of 
its  low  density,  would  increase  the  cost  of  flotation. 

4.  In  treating  the  round-table  feed  directly  by  flotation,  the  result- 
ing tailing  should  assay  0.30%  copper,  or  less,  with  a  concentrate 
carrying  not  over  40%   insoluble.     Possibly  the  concentrate  can  be 
made  much  cleaner  with  no  sacrifice  in  the  recovery. 

5.  It  is  thought  that  the  best  circuit-density  for  the  slime-pulp 
in  flotation  treatment  is  about  12%  solid. 

6.  It  is  thought  that  about  70°  F.  will  be  found  to  be  the  most 
economical  temperature  at  which  to  keep  the  pulp. 

7.  Acid  seems  to  be  absolutely  essential  to  the  successful  treat- 
ment by  flotation  of  our  slime. 

8.  The  addition  of  air  in  the  last  spitzkasten  is  of  no  advantage. 

9.  Any  considerable  increase  in  speed  of  the  agitators  above  a 
peripheral  speed  of  about  1300  ft.  per  min.  seems  to  be  disadvan- 
tageous.—  F.  Laist  and  A.  E.  Wiggin,  Trans.  A.  I.  M.  E. 


MECHANICAL    DEVELOPMENT  265 

MECHANICAL  DEVELOPMENT  IN  FLOTATION 

By  O.  C.  RALSTON 

A 

(Written  especially  for  this  volume) 

The  greater  number  of  inventions  that  have  appeared  in  connec- 
tion with  flotation  during  recent  years  have  been  of  a  mechanical 
nature.  Many  of  them  have  been  mistaken  by  the  uninitiated  as 
belonging  to  new  processes  but  usually  they  are  only  old  ideas  in  a 
slightly  changed  form.  The  more  ordinary  types  of  such  machines 
have  often  been  described  in  the  technical  press  and  so  will  be  omitted 
from  this  discussion  or  only  briefly  mentioned.  Many  of  them  are 
true  improvements  in  the  art  and  many  are  crude  modifications  of  a 
good  fundamental  type  designed  to  avoid  infringement. 

MECHANICAL  FROTH-MAKING  MACHINES.  In  froth-flotation  there 
are  many  ways  of  introducing  gas  into  the  pulp ;  one  of  the  oldest  and 
best  is  to  beat  air  into  the  pulp  by  the  use  of  rapidly  revolving  pro- 
pellers. 

Hoover's  book  gives  drawings  of  many  of  the  earlier  types  of 
machines.  These  have  been  used  so  often  in  later  papers  by  different 
writers  that  they  need  not  be  described  here.  Only  the  present 
standard  single-level  M.  S.  machine  need  be  shown.  See  Fig.  1  and  2. 
This  also  has  been  described  often.  The  only  thing  to  be  mentioned 
here  is  that  the  gears  on  the  drive-shaft  are  so  set  that  alternate  ones 
drive  the  impeller-shafts  in  opposite  directions  in  order  that  the  thrust 
on  the  drive-shaft  will  be  zero — an  important  point  in  design.  The 
drive-motors  are  usually  placed  at  the  head  of  the  machine  unless  hot 
pulp  is  being  used  or  acids  are  being  added,  in  which  case  the  motors 
are  placed  at  the  other  end  of  the  'machine,  so  as  to  avoid  steam  and 
corrosive  vapors.  Fig.  1  shows  two  standard  machines  placed  back 
to  back  in  order  to  economize  floor-space.  The  result  of  this  method  of 
placing  the  machines  and  the  method  of  conducting  away  the  concen- 
trate in  launders  is  indicated  in  Fig.  3,  which  shows  the  longitudinal 
section  of  the  slime-flotation  plant  at  Anaconda. 

By  making  the  impeller-shaft  horizontal  and  turning  the  blades  in 
a  vertical  plane,  G.  B.  Eberenz  and  J.  I.  Brown,  of  Cripple  Creek, 
claim  a  new  invention.  Their  machine  is  shown  in  Fig.  4,  which  is 
taken  from  their  patent  (U.  S.  1,187,822  of  June  20,  1916).  The 
patentees  make  the  following  claims :  The  blades  revolving  in  a  vertical 
plane  can  beat  air  into  the  pulp  more  effectively.  The  pulp  is  driven 
down  into  the  bottom  of  the  spitzkasten  instead  of  into  the  side,  as  is 


266 


FLOTATION 


FlG.    1.      STANDARD    M.    S.    MACHINES   PLACED  BACK   TO   HACK 


FlG.   2.      STANDARD    SINGLE-LEVEL   M.   S.    MACHINES 


MECHANICAL    DEVELOPMENT 


267 


268 


15 


FLOTATION 


, 


FIG.   4.      RBERENZ    &   BROWN    MACHINE 

usual  in  the  Minerals  Separation  machine.  A  better  churning-in  of 
the  oil  and  air  is  claimed  and  it  is  stated  that  in  practical  operation 
the  machine  makes  so  much  froth  through  the  action  of  the  agitators 
that  no  frothing-oil  is  necessary. 

Charles  E.  Rork,  of  Douglas,  Arizona,  invented  a  machine  that 


FIG.    5.      RORK    MACHINE 


M  KCJIANICAL    DEVELOPMENT 


269 


270  FLOTATION 

was  tested  in  several  of  the  mills  of  the  Phelps-Dodge  company, 
notably  the  Burro  Mountain  plant  at  Tyrone,  New  Mexico.  It  was 
patented  on  April  20,  1915,  and  the  patent  drawings  are  shown  in 
Fig.  5,  as  taken  from  U.  S.  1,136,485.  By  comparing  the  figures  it  can 
be  seen  that  in  the  machine  of  Eberenz  &  Brown  the  shaft  passes 
through  the  end  wall  of  the  machine  beneath  the  level  of  the  pulp 
while  in  Rork's  machine  the  shaft  is  above  the  level  of  the  pulp  and 
hence  not  subject  to  continual  abrasion,  leakage,  etc.  The  paddles 
merely  dip  into  the  pulp  and  throw  it  into  the  top  of  the  beating- 
chamber.  The  advantages  of  having  only  one  rotating  shaft  are  ob- 
vious, and  if  there  were  no  other  advantages  over  an  M.  S.  machine 
one  might  expect  this  machine  to  have  lower  maintenance  costs.  How- 
ever, a  disadvantage  has  been  discovered  in  having  such  a  long  shaft 
supporting  beating-blades  in  three  or  four  successive  compartments. 
This  shaft  is  likely  to  whip  unless  it  is  of  rather  large  diameter. 
Thus  the  length  of  the  machine  is  limited.  In  the  tests  at  Tyrone, 
Rork's  machine  was  found  to  use  more  power  than  had  been  expected. 
On  that  account  modifications  of  the  machine  were  made  until  it 
finally  resulted  in  the  form  shown  below.  This  is  now  known  and 
sold  as  the  K.  &  K.  machine,  named  after  the  inventors,  Max  Kraut 
and  F.  B.  Kollberg,  both  of  Douglas,  Arizona. 

By  expanding  Rork's  shaft  and  beaters  into  a  cylindrical  drum 
with  a  riffled  surface,  as  seen  in  Fig.  6,  considerable  longitudinal 
strength  was  gained  and  it  was  found  that  the  power-consumption 
was  considerably  lowered.  The  whirling  cylinder  dips  into  the  pulp 
and  the  air  is  trapped  between  the  riffles.  The  moving  part  is  almost 
perfectly  balanced  and  the  weight  of  entrained  pulp  is  relatively 
small.  The  low  consumption  of  power  is  a  natural  consequence  of 
this  design  and  raises  the  question  whether  other  machines  do  not 
whirl  all  of  the  pulp  to  their  disadvantage.  While  the  pulp  is  passing 
around  with  the  cylinder  of  the  K.  &  K.  machine  the  centrifugal 
force  is  tending  to  drive  it  out,  so  that  it  receives  a  considerable 
aeration  in  a  single  revolution  of  the  cylinder  and  is  thrown  through 
the  air  at  the  top,  to  drop  into  the  frothing-spitzkastens.  These  are 
four  in  number. 

This  machine  retains  all  of  the  advantages  and  eliminates  some  of 
the  troubles  of  the  Rork.  The  claim  is  made  that  it  requires  no  blow- 
ers, no  compressed  air,  and  no  pre-agitators.  As  far  as  pre-agitators 
are  concerned,  I  believe  that  any  machine  can  do  better  and  faster 
work  if  the  oil  is  already  well  disseminated  in  the  pulp  when  it  reaches 
the  flotation-machine.  Otherwise,  the  machine  is  extremely  simple 


MECHANICAL    DEVELOPMENT 


271 


SECTION 

-SHOWING 

UNLOADED      DRIVE 


SECTION 


PIG.  7.      JANNEY  MACHINE 


FLOTATION" 


MECHANICAL    DEVELOPMENT  273 

and  requires  only  a  single  belt-and-pulley  connection  to  a  source  of 
power.  The  inventors  claim  a  capacity  of  80  to  150  tons  per  24  hours 
with  10  to  15  horse-power.  These  figures  seem  low  and  have  caused 
many  engineers  to  doubt  their  reliability.  The  fact  that  these  ma- 
chines are  used  in  nearly  all  of  the  mills  of  the  Phelps-Dodge  com- 
panies would  indicate  that  they  must  have  decided  merit.  The  lively 
appearance  of  the  froth  is  very  attractive.  I  am  inclined  to  suspect 
that  with  low-grade  ores  these  machines  would  not  give  as  low  a 
tailing  as  other  machines,  although  they  are  known  to  make  a  high- 
grade  concentrate ;  therefore  it  seems  advisable  to  supplement  them 
by  pneumatic  machines,  to  glean  the  tailing. 

The  Janney  machines  are  of  two  types;  the  mechanical  and  the 
mechanical-air  cells.  Both  are  used  in  large  numbers  in  some  of  the 
largest  copper-concentrating  mills.  They  are  the  invention  of  T.  A. 
Janney,  mill-superintendent  of  the  Utah  Copper  Company. 

The  'mechanical'  machine  is  shown  in  Fig.  7.  This  shows  that  two 
impellers  are  used  on  the  same  shaft  and  that  the  pulp  is  agitated 
violently  against  baffles,  which  are  part  of  a  cast-iron  liner.  The 
whirling  of  the  pulp  over  the  top  of  the  liner  allows  it  to  flow  into  the 
spitzkasten,  of  which  there  are  two  for  each  agitation-chamber.  The 
agitator-shaft  is  a  continuation  of  the  motor-shaft,  being  screwed  into 
it,  and  revolves  with  the  motor  at  about  570  r.  p.  m.  The  first  machines 
were  made  of  one  main  casting  into  which  fitted  replaceable  liners,  but 
at  the  present  time  concrete  is  being  used  for  the  main  portion  of  the 
machine  and  cast  liners  are  used  to  protect  all  portions  subjected  to 
wear.  The  drawing  shows  two  circulating-pipes,  used  in  each  'spitz,' 
up  which  the  pulp  passes  to  the  agitation-chamber,  the  head  of  pulp 
in  the  'spitz'  being  such  that  the  pulp  enters  by  these  pipes  to  replace 
the  pulp  thrown  out  of  the  agitation-compartment.  Adjustable  gates 
between  the  adjacent  spitzkasten  allow  the  pulp  to  pass  from  one 
cell  to  the  next  by  gravity.  However,  the  circulating-pipes  permit  the 
repeated  treatment  of  most  of  the  pulp  in  each  .cell  before  it  passes 
to  the  next  one.  The  drawing  also  shows  a  good  design  of  a  froth-re- 
mover which  allows  any  depth  or  length  of  stroke. 

Since  these  cells  are  separately  constructed  they  $an  be  installed 
in  a  variety  of  ways  to  suit  the  convenience  of  the  designer.  Fig.  8 
shows  part  of  an  equipment  of  two  mixers  and  15  cells  in  a  row. 
The  feed  is  split  between  the  first  five  cells.  These  make  clean  froth. 
The  tailing  then  passes  in  series  through  the  remaining  cells,  which 
make  middling.  This  is  called  the  'multiple-series'  arrangement.  The 
machine  is  especially  adapted  to  the  flotation  of  coarse  material  such 


FLOTATION 


as  low-grade  concentrate  produced  by  vanners  and  the  like.  The  per- 
centage of  solid  in  such  feed  should  range  between  20  and  23.  The  mo- 
tors use  about  10  hp.  each,  consequently  an  installation  of  this  type  of 
machine  requires  more  power  than  almost  any  other  standard  device 


MECHANICAL    DEVELOPM  KNT 


275 


1. 


K' 


JJ, 


o 


J 


FlG.  11.     THE  OWEN  MACHINE 


276 


FLOTATION 


FlG     12.       THE    H1QOIN6       CACHINE 


MECHANICAL    DEVELOPMENT 


277 


used  for  flotation.     On  that  account,  the  later  'mechanical-air'  cell 
has  displaced  it  to  a  great  extent. 

The  mechanical-air  cell,  as  shown  in  Fig.  8,  likewise  utilizes  a  ver- 
tical-shaft motor  set  directly  over  the  agitation-compartment.  The 
impeller-shaft  is  a  continuation  of  the  motor-shaft.  The  bottoms  of  the 
spitzkasten'  are  covered  with  a  slanting  air-mat,  similar  in  construction 
to  that  in  Callow  cells.  A  pneumatic  froth  is  produced,  which  flows 


FlG.    13.       WOOD    SUB-AERATION    MACHINE 


over  the  discharge-lip  of  each  'spitz'  without  the  necessity  of  a  skim- 
mer. The  tailing  drops  into  a  box-like  arrangement  at  the  foot  of  the 
air-mat  and  thence  passes  up  over  a  weir  of  adjustable  height  (not 
shown) .  The  adjustment  of  the  height  of  this  weir  regulates  the  depth 
of  pulp  in  the  spitz.  Usually,  the  weirs  require  little  manipulation 
after  once  being  set  to  give  proper  depth  of  froth. 

The  motor  uses  less  power  than  that  of  the  mechanical  machine, 
averaging  7  hp.  per  cell.    About  150  cu.  ft.  of  air  per  minute  at  four 


278 


FLOTATION 


to  five  pounds  pressure  per  square  inch  is  needed  for  each  machine. 
Two  operators  can  easily  serve  a  unit  of  3000  tons  and  have  to  adjust 
only  the  amount  of  air  in  the  wind-boxes  and  occasionally  the  oil-feed. 
These  machines  are  placed  either  side  by  side  or  end  to  end,  accord- 
ing tc  the  preference  of  the  designer.  About  five  of  them  in  series  are 
used  for  roughing  and  two  for  cleaning.  Such  an  equipment,  together 


FlG.   14.      ANOTHER  DESIGN  OF  WOOD  MACHINE 

with  an  emulsifier,  treats  150  to  200  tons  per  24  hours.  By  decreasing 
the  amount  of  air  it  is  possible  to  raise  the  grade  of  the  concentrate, 
but  the  tonnage  is  lowered. 

The  main  wearing-parts  are  the  impellers  and  the  liners.  A  liner 
will  last  from  three  to  five  months  and  the  impellers  two  to  three 
months.  A  single  cell  can  be  shut-down  for  repairs  without  disturb- 
ing the  operation  of  the  others  since  there  is  a  drop  of  three  feet  be- 
tween them.  The  motor  is  lifted  off  with  a  small  crane,  exposing  the 


_AJ  ECHAXICAL    DEVELOPMENT 


279 


280 


FLOTATION 


M  ECU  AN  10  AL    DEVELOPMENT  281 

inside  of  the  agitator-chamber.  Replacing  a  liner  or  screwing  on  a  new 
shaft  with  new  impellers  occupies  only  about  20  minutes.  Hence 
practically  continuous  operation  is  possible. 

Since  each  cell  has  an  agitating-compartment  oil  may  be  added  at 
any  step  in  the  series. 

The  use  of  individual  motor-drive  for  flotation  cells  is  parallel  with 
the  tendency  to  do  the  same  with  grinding  and  concentrating  machin- 
ery. The  designers  claim  that  the  first  cost  is  not  excessive  when 
compared  with  the  cost  of  belting,  shafting,  and  super-structure  nec- 
essary for  a  group-drive.  When  shafting  is  used  in  a  group-drive  the 
settling  of  buildings  and  other  causes  bring  about  friction  in  the  bear- 
ings that  support  the  shafting.  Stopping  to  true-up  requires  a  shut- 
down of  the  mill,  and  this  is  generally  not  done.  The  individual-motor 
drive  eliminates  all  such  difficulties  and  removes  a  great  deal  of  super- 
structure, so  that  a  small  crane  can  have  proper  access  to  the  cells. 

The  great  disadvantage  of  the  Janney  machine  is  its  excessive  use 
of  power.  Where  power  is  cheap  the  cost  is  low  but  in  other  localities 
this  item  is  very  important.  I  also  question  the  advisibility  of  using 
agitators  after  dissemination  of  the  oil  in  the  pulp  has  been  accom- 
plished. The  porous  blanket  cells  will  then  froth  out  all  the  mineral 
without  the  necessity  of  using  more  power  for  agitation.  I  am  in- 
debted to  E.  Shores  of  the  Stimpson  Equipment  Co.,  which  makes 
these  machines,  for  much  of  my  information  and  for  the  drawings. 

SUB-AERATION  MACHINES.  The  mention  of  the  use  of  air-baskets  in 
spitzkastens  of  the  Janney  machine  suggests  the  many  devices  that  call 
for  the  use  of  moving  blades  in  the  pulp  and  the  introduction  of  air. 
After  all,  the  thing  desired  is  to  so  attach  air  or  gas  bubbles  to  valuable 
mineral  particles  that  they  will  be  floated  in  a  froth.  Whether  atmos- 
pheric air  be  beaten  into  the  pulp  by  mechanical  swirling  or  whether 
compressed  air  be  introduced  into  the  pulp  close  to  the  swirling  blades, 
the  result  is  that  bubbles  of  air  are  caught  in  the  pulp  in  front  of  the 
impellers  and  are  disseminated  through  the  pulp. 

A.  H.  Higgins  and  W.  W.  Stenning  invented  one  of  the  first  sub- 
aeration  machines  used  in  the  United  States  by  the  Minerals  Separa- 
tion, Ltd.  It  was  protected  by  U.  S.  1,155,815  of  October  5,  1915,  from 
which  is  taken  Fig.  10.  The  reason  for  the  designing  of  such  a  ma- 
chine is  given  in  the  words  of  the  patentees : 

"One  object  of  this  invention  is  to  provide  an  apparatus  in  which 
agitation,  aeration,  froth  formation,  and  froth  separation  are  effected 
in  one  box  or  series  of  boxes  without  requiring  the  use  of  spitzkasten. 
A  further  object  is  to  remove  the  froths  immediately  they  are  formed 


282 


FLOTATION 


so  that  a  mineral-bearing  froth  ready  for  flotation  shall  not  be  sub- 
jected to  further  agitation  with  the  pulp.  An  incidental  object  is  to 
effect  the  efficient  recovery  of  so-called  'tender'  froths  from  which 
the  mineral  has  a  .tendency  to  shower. ' ' 

These  objects  are  attained  by  introducing  air  beneath  the  impellers 
through  the  pipes  E.  The  impellers  beat  the  stream  of  air-bubbles 
into  a  fine  froth,  which  immediately  rises  and  strikes  the  inclined 
baffle  J,  which  directs  it  to  the  left  into  the  box  K.  The  pulp  issues 
into  the  upper  half  of  this  box  from  the  box  K  through  the  openings  L 


FlG.    17.      SECTION   OF   MISCHLEB   MACHINE 


arid  the  froth  rises  to  the  surface,  while  the  pulp  in  this  relatively 
quiet  zone  sinks  to  the  top  of  the  baffle  J  and  is  deflected  to  the  right, 
passing  through  opening  F  into  the  bottom  of  the  next  compartment. 
The  drawing  shows  the  compartment  farthest  to  the  left  as  a  mixing- 
compartment  without  any  froth-overfloAV.  Two  different  shapes  of 
impeller-blades  are  also  shown.  The  first  of  these  machines  was  made 
with  the  air-pipes  E  open  to  the  air,  with  the  expectation  that  the 
violent  rotation  of  the  impellers  would  create  enough  suction  to  pull 
air  into  these  pipes.  This  expectation  was  never  justified  arid  com- 
pressed air  was  found  necessary.  Further,  the  glands  where  the 
impeller-shaft  passed  through  the  inclined  baffles  wore  out  fast  and 
admitted  too  much  air.  The  impeller-blades  and  liners  of  the  beating- 
boxes  wear  out  soon  and  are  inaccessible,  and  the  machine  must  be 


MECHANICAL    DEVELOPMENT  283 

taken  apart  in  order  to  replace  them.  On  that  account  this  particular 
type  of  sub-aeration  cell  is  not  now  being  used,  although  a  machine  of 
this  pattern  was  employed  for  a  while  at  Anaconda. 

T.  M.  Owen  has  invented  a  much  more  practical  machine  which  is 
protected  by  U.  S.  1.155,836  of  October  5,  1915.  Air  is  admitted 
beneath  the  impeller  through  the  valve  O  and  the  pulp  is  fed  into  the 
machine  through  the  pipe  M.  The  froth  rises  as  soon  as  it  is  formed, 
as  can  be  seen  in  Fig.  11.  The  zone  below  the  baffles  El  is  violently 
agitated,  but  the  baffles  prevent  the  disturbance  reaching  the  upper 
portion  of  the  cell  and  the  froth  has  a  chance  to  separate  quietly  from 
the  pulp.  It  overflows  into  the  lander  Q  and  the  tailing  passes  out  of 
pipe  T.  This  machine  is  accessible  for  repairs,  as  can  be  seen  by  look- 
ing at  the  section  taken  through  the  line  3-3.  Moreover,  the  construc- 
tion is  simple,  being  especially  adapted  to  steel-work.  The  constricted 
top  is  characteristic  of  machinery  often  used  in  differential  flotation, 
in  which  a  minimum  amount  of  oil  is  added  in  order  to  cause  flotation 
of  only  one  mineral,  and  excessive  aeration  is  necessary  to  build  up 
any  depth  of  froth  whatever,  on  account  of  its  tendency  to* break. 

A.  H.  Higgins  gives  alternative  designs  of  many  similar  sub- 
aeration  machines  in  U.  S.  patent  1,155,816  of  October  5,  1915.  These 
are  shown  in  Fig.  12.  In  each  case  the  air-inlet  is  lettered  E,  the 
pulp-inlet  D,  and  the  tailing-discharge  J. 

The  patentee  claims  the  following  advantages  for  this  kind  of 
machine :  It  is  possible  to  regulate  the  amount  of  gas  employed  for 
gaseous  selection  and  flotation.  It  is  also  possible  to  regulate  the 
degree  of  division  of  the  air  by  the  form  and  speed  of  the  agitator. 
These  are  of  great  importance,  as  Higgins  claims  that  different  ores 
and  different  characters  of  suspended  particles  are  considerably  af- 
fected by  the  total  amount  of  air  or  its  degree  of  division.  Further, 
the  amount  of  frothing-agent  to  be  used  with  this  apparatus  may  be 
considerably  reduced  from  that  necessary  in  the  usual  apparatus  for 
the  agitation-froth  process.  It  is  characteristic  of  this  apparatus  that 
it  has  a  continuous  admission  of  air  at  the  bottom  and  continuous 
feed  and  overflow  above,  so  that  the  upper  part  of  the  pulp  is  in  a  state 
of  comparative  quiet  although  reinforced  constantly  by  a  stream 
of  rising  bubbles,  so  that  it  overflows  continuously. 

The  Hebbard  sub-aeration  machine  is  an  even  simpler  type  of  con- 
struction. A  long  series  of  compartments  like  the  standard  mechan- 
ical type  of  M.  S.  machine  is  used,  except  that  large  openings  are  cut 
in  the  walls  between  the  adjacent  agitation  compartments  and  the 
spitzkastens  have  been  omitted.  A  deep  heavy  grid  is  placed  in  each 


284 


FLOTATION 


agitation  compartment  above  the  impellers  and  air  is  introduced  under 
each  impeller.  The  froth  overflows  from  each  compartment  into  a 
launder.  This  machine  is  in  fairly  common  use  on  account  of  its 
simple  construction. 

The  Hebbard-Harvey  sub-aeration  machine  is  an  improvement  on 
the  Hebbard  machine  made  by  R.  J.  Harvey  of  the  Central  mine  at 
Broken  Hill.  The  impellers  are  driven  by  shafts  passing  up  through 
the  bottom  of  the  machine  instead  of  coming  down  from  above.  This 
removes  the  unsightly  structure  above  the  machine  and  allows  free 


C 


FlG.    18.       SECTION    OF   OWEN    MACHINE 

access  to  the  top  but  necessitates  the  maintenance  of  a  packed  gland 
for  each  impeller-shaft. 

The  L.  A.  Wood  sub-aeration  machine  is  a  somewhat  different 
design,  said  to  be  adapted  to  floating  sulphides  and  other  minerals  by 
use  of  air  and  without  the  addition  of  a  frothing-agent  or  an  oil. 
This  is  shown  in  Fig.  13,  which  is  taken  from  the  patent  specification, 
U.  S.  1,155,861  of  October  5,  1915.  The  air-bubbles  with  their  asso- 
ciated mineral  break ;  hence  a  baffle  E  is  necessary  to  catch  them.  The 
pulp-inlet  is  at  H  and  the  outlet  at  J.  Fig.  14  is  another  design, 
covered  by  British  patent  10,312  of  1914,  also  granted  to  Wood.  The 
process  is  described  as  being  applicable  to  the  flotation  of  sulphide  ores 
of  copper  in  neutral  pulp  at  ordinary  temperatures;  but  it  has  been 
applied  to  Broken  Hill  tailing  with  the  addition  of  \%  sulphuric  acid, 
and  heating  to  60°  C.  is  recommended.  Differential  flotation  is  also 


MECHANICAL    DEVELOPMENT  285 

claimed  by  varying  the  aeration  according  to  the  nature  of  the  ore 
and  the  degree  of  crushing.  These  patents  are  assigned  to  Minerals 
Separation. 

W.  Fagergren  and  W.  D.  Green,  under  U.  S.  1,195,453  of  August 
22,  1916,  have  shown  still  another  design  of  sub-aeration  machine. 
Its  chief  claim  is  simplicity  of  construction,  being  made  of  plain 
lumber,  as  can  be  seen  in  Fig.  15. 

R.  T.  Mischler,  metallurgist  for  the  El  Tigre  mine,  in  Sonora, 
Mexico,  has  patented  a  machine  in  which  the  agitation-shaft  is  hori- 
zontal and  submerged.  Fig.  16  and  17  give  a  general  idea  of  the  con- 
struction. The  pulp-inlet  is  at  191  and  the  air-inlet  is  through  pipe 
160  and  valve  176.  The  construction  seems  to  be  involved  and  in- 
accessible although  the  bolted  plate  185,  shown  in  the  cross-section,  can 
be  taken  off  for  inspection  and  replacement  of  the  agitators  or  agi- 
tator-chamber lining.  The  patentee  states  that  the  objects  of  the  in- 
vention are,  "First:  To  separate  the  concentrate  from  the  gangue 
during  a  repeated  agitation  of  the  pulp,  in  the  presence  of  air  or  other 
gas,  such  agitation  being  followed  by  a  period  of  quiescence  or  separa- 
tion, when  the  concentrate  rises  to  the  surface,  and  overflowing,  while 
the  gangue  settles  to  the  bottom  and  is  subjected  to  agitation  and 
separation  during  successive  alternating  periods,  in  order  to  remove 
the  remaining  traces  of  the  concentrate.  Second :  In  an  apparatus 
of  the  character  described,  to  provide  a  series  of  alternating  agitation 
and  separation  chambers.  Third :  To  maintain  a  minimum  power 
consumption,  by  simultaneous  agitation  of  the  gangue  in  the  agitation 
chambers.  Fourth :  To  obtain  maximum  extraction  and  grade  of 
concentrate  by  agitation  of  the  gangue,  in  the  presence  of  air  or  other 
gas,  and  under  the  pressure  of  a  considerable  height  of  pulp,  thereby 
obtaining  the  advantage  of  the  expansion  of  the  gas  bubbles,  as  they 
rise  to  the  surface,  carrying  the  concentrate.  Fifth :  To  obtain  from 
the  impulses  imparted  to  the  pulp  by  the  agitation  in  all  of  the  separa- 
tion chambers,  an  approximately  uniform  overflow  level  for  the  con- 
centrate. Sixth :  To  prevent  resettling  of  the  concentrate,  by  minimiz- 
ing agitation  in  the  separation  chambers.  Seventh :  To  prevent  the 
settlement  of  sand,  and  the  consequent  clogging  of  the  apparatus ;  and 
Eighth :  To  transfer  the  pulp  from  one  chamber  to  another  within 
zones  of  intense  pulp  agitation. ' ' 

Mischler 's  machine  is  covered  by  U.  S.  1,197,843  of  September  12. 
1916.  Pie  claims  that  the  novel  principle  of  his  invention  consists  in 
the  agitation  of  the  pulp,  while  submerged,  with  introduction  of  gas 
at  a  considerable  distance  below  the  surface  and  under  a  considerable 


286 


FLOTATION 


pressure  of  pulp.  This  means  a  greater  volume  of  air  per  unit-volume 
of  pulp  than  is  possible  when  air  is  merely  being  churned  into  the  pulp 
at  the  surface.  He  also  claims  that  a  cleaner  concentrate  is  produced 
by  the  rupture  at  the  surface  of  a  portion  of  the  sulphide-bearing 
bubbles,  the  concentrate  thus  liberated  attaching  itself  to  the  under- 
lying bubbles,  while  the  liberated  gangue  slides  from  their  surfaces. 


FlG.   19.      CALLOW  PNEUMATIC   MACHINE 

The  introduction  of  air  into  the  suction  of  a  centrifugal  pump 
through  which  the  pulp  is  passing  constitutes  another  method  of  sub- 
aeration.  One  way  of  carrying  this  into  effect  in  a  continuous  plant  is 
shown  in  the  patent  of  T.  M.  Owen  (U.  S.  1,157,176  of  October  19, 
1915).  The  pulp  is  mixed  with  the  oil^and  other  addition-agents  in 


MECHANICAL    DEVELOPMENT  287 

tank  F  (See  Fig.  18)  and  the  air  enters  the  pulp-stream  through 
the  pipe  L.  The  pump  discharges  into  a  frothing-box  and  the  tailing 
passes  out  at  O  into  the  suction  of  the  next  pump.  Any  number  of 
flotation-cells  of  this  construction  can  be  used  in  series.  A  crowding 
cone  C  can  be  used  when  the  froth  is  brittle  or  thin.  In  this  way  a 
close  control  of  the  aeration  is  possible.  Owen  recommends  this 
apparatus  for  differential  flotation. 

The  centrifugal  pump  is  also  used  in  the  Bunker  Hill  &  Sullivan 
mill  in  a  machine  similar  to  that  of  Owen,  but  this  machine,  the  in- 
vention of  R.  S.  Handy,  is  of  more  simple  construction.  The  froth- 
boxes  are  built  into  one  long  box  with  partitions  in  which  spaces  are 
left  for  the  gravitation  of  the  pulp  from  one  compartment  into 
another.  A  centrifugal  pump,  into  whose  suction  a  compressed-air 
pipe  is  led,  draws  the  pulp  from  the  bottom  of  each  pair  of  froth- 
boxes  and  returns  it  about  half-way  up  the  side.  The  froth  rises  and 
is  removed  by  an  endless  belt  with  attached  rakes.  Where  pneumatic 
machines  gave  a  concentrate  of  40%  lead  this  machine  gives  a  con- 
centrate of  nearly  60%  lead,  the  restricted  agitation  causing  a  clean 
froth  to  form.  Turning  the  air-valve  slightly  in  either  direction  is 
often  enough  to  spoil  the  froth. 

Sub-aeration  machines  are  now  much  more  popular  than  the  older 
standard  mechanical  machines,  because  the  use  of  them  decreases  the 
consumption  of  power  and  also  of  oil.  Higher  recoveries  likewise  are 
obtained.  Undoubtedly  the  introduction  of  compressed  air  in  flotation- 
cells  usually  benefits  the  operation.  Only  with  an  ore  or  a  frothing- 
agent  that  gives  too  much  froth  is  sub-aeration  a  disadvantage. 

PNEUMATIC  FLOTATION  MACHINES.  The  use  of  air  for  flotation, 
without  mechanical  methods  for  breaking  up  the  bubbles,  has  under- 
gone notable  development  during  the  last  two  years.  At  first,  the 
machines  were  provided  with  porous  media  for  introducing  the  air 
into  the  pulp,  but  later  this  was  not  always  found  necessary.  On 
that  account  pneumatic  machines  may  be  divided  into  two  classes, 
one  in  which  a  porous  medium  is  used  and  the  other  in  which  the  air 
is  introduced  through  jets  or  under  pressure. 

The  standard  Callow  machine  is  the  invention  of  J.  M.  Callow, 
one  of  the  pioneers  in  pneumatic  flotation.  One  fairly  common 
design  of  this  machine  is  shown  in  Fig.  19  together  with  the  Pachuca 
in  which  the  oil  is  mixed  into  the  pulp  previous  to  flotation.  The 
eight  air-distributing  boxes  at  the- bottom  are  usually  cast  in  one  block 
and  the  bottom  is  unbolted  and  removed  when  the  canvas  needs  re- 
placement. Punched-iron  plates  are  shown  supporting  the  canvas 


288 


FLOTATION 


rigidly.  Sometimes  the  canvas  is  overlaid  by  wire-screen  instead  of  the 
punched-iron  plates  to  prevent  its  bulging  out  or  breaking  under  the 
air-pressure,  or  the  canvas  is  stretched,  tightly  and  is  not  otherwise 
supported.  The  construction  of  the  bottom  also  varies  in  the  manner 
of  holding  the  canvas  in  place.  In  the  drawing  it  is  clamped  between 
punched-iron  plates.  It  may  be  clamped  with  a  special  frame  that 
goes  over  each  wind-box ;  or  a  groove  is  cut  into  the  frame  all  the  way 
around  each  wind-box  and  the  canvas  is  driven  into  this  groove  and 
held  tightly  by  pounding  in  a  solid  rope  slightly  greater  in  diameter 
than  the  groove.  For  removal  the  rope  is  merely  pulled  out  and  a  new 
canvas  can  then  be  placed  and  roped  in. 

The  round  type  of  Callow  cell,  Fig.  20,  was  one  of  the  earlier  forms 
tested  by  him  and  was  protected  by  U.  S.  1,141,377  of  June  1,  1915. 
A  carborundum  stone  was  used  as  the  porous  bottom;  it  was  satis- 


FlG.    20.      ROUND   TYPE  Of  CALLOW   CELL 


MECHANICAL    DEVELOPMENT 


289 


factory  except  that  the  continued  use  tended  to  cause  the  pores  to 
choke  with  dirt  and  grit.  'Filtros'  blocks  suffered  the  same  fate. 
Canvas  was  found  best  for  this  work  and  was  later  u^ed  in  all  the 
standard  machines.  Hence  there  was  no  more  necessity  for  building 
the  machine  round,  to  accommodate  the  use  of  a  carborundum  wheel. 
The  canvas  is  usually  discarded  after  about  six  months,  for  by  that 
time  it  has  become  clogged  with  ore-particles,  by  grease  from  the 
blower,  or  by  dust  from  the  air.  In  the  Chino  and  Utah  Copper 
mills  the  air  is  filtered  through  cloth  by  encasing  the  blower  in  a  room 


FlG.  21.      CALLOW  FLAT-BOTTOM  CELL 

with  walls  of  muslin.  Trouble  is  caused  if  the  air  is  turned  off  while 
a  pneumatic  machine  is  full  of  pulp  and  the  machine  is  allowed  to 
stand  for  a  number  of  hours.  In  this  case  the  fine  slime  has  an  oppor- 
tunity to  settle  upon  the  canvas  and  cake  in  its  pores.  Canvas,  being 
pliable,  clears  itself  of  such  obstruction  much  more  easily  than  rigid 
carborundum  or  'filtros'  blocks. 

The  Callow  flat-bottom  cell,  U.  S.  1,182,748  of  May  9,  1916,  is 
shown  in  Fig.  21.  The  sand  is  advanced  over  the  bottom  by  the  use  of 
a  drag-belt.  It  is  not  certain  that  this  is  necessary,  for  the  Inspiration 
machine,  described  elsewhere,  has  a  flat  bottom  and  the  sand  slides 
gradually  across  the  canvas.  I  have  seen  such  a  flat-bottomed  cell  in 
use  without  a  drag-belt. 


290 


FLOTATION 


The  tripple-length  Callow  cell  has  more  recently  been  devised  for 
treatment  of  the  finely  divided  slime  of  the  Cobalt  district.  It  is  29 
ft.  long  and  is»made  from  castings  intended  for  three  of  the  standard- 
length  cells.  Only  pulps  containing  small  percentages  of  sand  can  be 
used,  as  the  slope  of  the  machine  is  much  reduced. 


I 

I 


James  M.  Hyde  has  described  a  pneumatic  flotation  machine  in  the 
Mining  and  Scientific  Press  of  August  5,  1916.  The  individual  wind- 
boxes  can  be  removed  without  disturbing  the  others  so  that  the  ma- 
chine can  be  run  continuously  while  any  one  of  them  is  removed  for 
replacement  of  the  canvas.  The  essentials  of  this  machine  are  shown 
in  Fig.  22  and  23.  By  having  the  air-inlet  valves  directly  above  the 


M  K< '  1 1  A  \1CAL    DEVELOPMENT 


291 


!92 


FLOTATION 


froth  in  the  cell  there  can  be  no  excuse  for  operators  allowing  the  dis- 
tribution of  air  to  become  uneven. 


Toilinas 
Discharge  -< 


FIG.    24.      LAUNDER   OB   CRERAR    MACHINE 


Airtight^ 


Airtight — > 


^>l|<5'>l<---//"-->l  I    Section  through  End 

'   -. B'-Sg-- - - ~>J     of  Air  Distributor 

Plan  of  Air  Distributor  J] 

njj  Acetylene  Welded 


,    ; 
I     ) 

1  L 


, 

Side  View,  Showinq  Section  of  One  End 
FIG.   25.      SHEET-STEEL  BOTTOMS  OF  WIND-BOXES 

A  similar  machine,  used  in  the  Inspiration  mill,  was  likewise  de- 
veloped from  the  fundamental  conception  of  using  a  launder  with  a 
porous  bottom.  Its  evolution  is  graphically  illustrated  by  Fig.  26, 
which  is  taken  from  the  paper  by  Rudolf  Gahl  presented  at  the  Sep- 


MECHANICAL    DEVELOPMENT 


293 


tember  meeting  of  the  American  Institute  of  Mining  Engineers  in 
1916.  The  details  of  the  machine  are  given  in  Fig.  27.  It  consists 
of  a  series  of  boxes  with  false  bottoms  of  canvas  in  which  frothing  is 
produced  by  compressed  air  introduced  beneath  the  canvas.  The 
pulp  goes  from  one  cell  to  the  next  by  passing  underneath  the  parti- 
tion between  the  two  boxes.  This  arrangement  has  the  advantage  of 
giving  a  treatment  in  series,  forming  a  rougher-froth,  which  is  re- 
treated in  a  similar  set  of  cells.  The  sand  tends  to  settle  in  this 


Tailings  Launder 

PLAN 


^ 


ELEVATION 


-Baffles- 


PLAN 


Froth  Overflow 

Froth  Overflow 

Froth  Overflow 

Froth  Overflow 

*. 

1 

x- 

^IH—  ^ 

^—  ll^ 

j££~^S< 

^     : 

( 

ELEVATION 

PlG.    26.      DIAGRAM    SHOWING  ORIGIN   AND  DEVELOPMENT   OF   INSPIRATION 
FLOTATION    MACHINE 


machine  and  at  present  is  stirred  occasionally  by  the  introduction  of 
a  pipe  on  the  end  of  a  hose,  injecting  water  under  80-lb.  pressure. 
The  machine  has  the  advantage  of  great  compactness  and  is  easily 
repaired.  The  bottom  of  each  cell  can  be  removed  without  stopping, 
as  the  air-line  is  led  down  to  each  individual  air-box  in  a  manner 
similar  to  the  Hyde  machine,  above  described. 


294  FLOTATION 

It  is  believed  that  the  principal  advantage  of  the  Inspiration 
machine  is  the  large  tonnage  that  can  be  treated  on  a  given  floor-space. 
Being  almost  flat-bottomed  the  sand  tends  to  collect  on  the  canvas  and 
two  or  three  laborers  on  each  shift  are  kept  busy  passing  a  small  pipe 
with  high-pressure  water-jets  over  the  surfaces  of  the  canvas  bottoms 
in  each  compartment  in  order  to  stir  the  sand  and  cause  it  to  pass  on. 
For  a  plant  of  the  size  of  that  at  Inspiration  the  increased  cost  per  ton 
due  to  this  extra  labor  is  small.  The  individual  air-baskets  make 
possible  the  removal  and  replacement  of  the  canvas  squares  without 
stopping  the  machine,  one  compartment  merely  running  empty  and 
overflowing  no  froth. 

The  Launder,  or  Crerar,  machine  is  one  in  which  the  pulp  passes 
through  a  considerable  length  of  launder.  It  is  adapted,  as  can  be  in- 
ferred, to  making  a  low  tailing  owing  to  the  length  of  time  that  the 
pulp  is  in  the  machine.  The  speed  of  advance  of  the  pulp  through 
the  machine,  however,  is  faster  than  in  the  Callow  type  in  order  to 
obtain  the  same  tonnage.  The  description  of  this  machine  is  taken 
from  the  Engineering  and  Mining  Journal,  of  December  16,  1916, 
where  it  was  described  by  B.  M.  Snyder.  See  Fig.  24.  It  consists  of  a 
series  of  six  launders  6  ft.  long  by  14  in.  wide,  placed  side  by  side, 
connected  in  series  with  sufficient  space  between  to  allow  for  removal 
of  froth.  These  are  also  successively  deeper  in  order  to  induce  a  flow 
of  pulp.  Fig.  25  shows  the  construction  of  the  sheet-steel  bottoms  of 
the  wind-boxes,  which  are  easily  made  at  the  workshop  of  an  ordinary 
mill.  The  total  cost  of  construction  of  such  a  machine  is  estimated  at 
$458.  The  air  required  is  10  cu.  ft.  per  minute  per  square  foot  of 
frothing-area  at  3  to  5  Ib.  per  sq.  in.  This  gives  an  average  of  about 
60  tons  daily  capacity. 

The  Fynn-Towne  or  bubble-column  machine  was  one  of  those  used 
during  the  period  of  competitive  testing  at  Inspiration.  It  consists  of 
a  deep  column  for  pulp  with  a  porous  carborundum  stone  at  the  bottom 
fo-r  the  admittance  of  atomized  air.  The  machine  did  not  do  as  well  as 
did  the  Callow  machine  during  the  Inspiration  testing  so  it  was  dis- 
carded by  that  company. 

The  C-B  frothing-classifier,  invented  by  David  Cole  and  Julius 
Bergman,  of  El  Paso,  is  shown  in  Fig.  28  and  29.  Compressed  air  is 
introduced  into  the  cell  through  perforated  pipes  which  are  wrapped 
with  canvas  to  further  break  up  the  streams  of  air.  A  series  of  these 
pipes  is  used  near  the  bottom  of  the  cell,  as  seen  in  Fig.  28,  but  enough 
space  is  left  for  the  sand  to  drop  between  the  pipes  and  pass  out  of 
the  cell.  Hence  this  type  of  machine  is  not  troubled  by  the  sand  in 


M  K C  J  f  A  N I C  A  L    D  E  V  R  T,O PM  E  N T 


295 


296 


FLOTATION 


the  pulp.  The  coarse  mineral  in  the  sand  is  table-concentrated  after 
the  slime  has  been  floated. 

In  U.  S.  patent  1,201,934  of  October  17,  1916,  Callow  gives  a  mod- 
ification of  his  standard  cell  in  which  sand  is  spigoted  out  at  21  (see 
Fig.  30)  and  the  slime  passes  out  of  a  separate  pipe,  marked  24.  The 
sand  can  then  be  tabled  and  the  slime  treated  further  by  flotation. 

It  was  soon  found  that  the  size  of  the  bubbles  produced  by  porous 
media  depended  more  on  the  composition  of  the  solution  into  which 
they  were  blown  than  on  the  size  of  the  holes  in  the  medium.  A  rapidly 
moving  jet  of  air  or  gas  was  found  to  be  fairly  well  emulsified  if  water 


FlG.    28.       CROSS-SECTION    OF    C-B    TUBE-GRATE    FLOTATION-CELL 


containing  a  frothing-agent  was  used.     A  number  of  machines  have 
been  designed  to  utilize  this  principle. 

Dudley  H.  Norris  invented  the  'pressure'  machine  shown  in  Fig. 
31,  taken  from  U.  S.  1,167,835  of  January  11,  1916.  Water  is  fed  into 
an  injector-tube  7  and  air  is  entrained  from  tube  8,  so  that  water  with 
an  excess  of  air  is  allowed  to  collect  under  pressure  in  4.  When  this 
water  with  an  excess  of  dissolved  air  is  released  in  the  flotation -tank 
the  released  pressure  allows  the  dissolved  air  to  appear  in  the  form  of 
bubbles  in  a  fine  state  of  division.  Mr.  Norris  states  that  he  first  had 
the  idea  when  noticing  the  water  in  the  wash-room  of  a  Pullman  car 
made  milky  by  dissolved  air.  As  is  well  known,  the  water-tank  of  a 
Pullman  car  is  underneath  and  air  from  the  brake-system  is  used  to 
force  it  into  the  faucets.  As  far  as  Ircan  learn  this  machine  is  not 


MECHANICAL    DEVELOPMENT 


297 


now  used  in  any  mill,  but  it  is  suggestive  and  very  much  like  some 
machines  now  in  use. 

G.  E.  Ohrn  has  invented  a  machine  shown  in  Fig.  32  taken  from 
his  patent  U.  S.  1,187,772  of  June  20,  1916.    A  jet  of  steam  is  fed  by 


FlG.   29.      LONGITUDINAL   SECTION  OF  C-B   FLOTATION    MACHINE 
THREE  CELLS   IN    SERIES 

the  pipe  D  and  the  oil  is  allowed  to  enter  through  the  small  inner  pipe 
E.  The  jet  plunges  into  the  pulp  and  air  is  entrained  around  the 
steam- jet.  The  resulting  froth  must  pass  a  jet  of  water  L  arranged  to 
wash  out  any  gangue  that  tends  to  stick  in  the  mineral  froth.  /  is  the 


298 


FLOTATION 


MECHANICAL    DEVELOPMENT 


299 


FIG.    31.       NORRIS    PRKSSURE    MACHINE 


300 


FLOTATION 


froth-overflow  launder  and  K  is  the  tailing-discharge.  A  central  baftie 
can  be  used  to  allow  slime  to  overflow  separately  from  the  sand.  The 
feed,  if  desired,  can  be  led  into  hopper  B.  The  steam  tends  to  vaporize 
some  of  the  oil  and  spread  it  over  a  greater  amount  of  pulp.  This  ma- 
chine was  assigned  by  the  Swedish  inventor  to  Minerals  Separation  as 
was  also  his  British  patent.  So  far  as  can  be  learned  the  machine  is  not 
in  use  on  this  side  of  the  Atlantic  but  the  figures  on  its  operation  in 
Sweden,  given  out  by  local  promoters,  look  most  interesting.  However, 
steam  is  a  rather  expensive  medium  to  use  for  mixing  pulp. 

Another  steam-jet  machine  has  been  patented  by  Gustaf  Grondal, 


2T- 


FlG.    32.      THE  OHRN    MACHINE 

another  Swede,  under  U.  S.  1,202,512  of  October  24,  1916.  The  draw- 
ing in  Fig.  33  is  taken  from  the  patent  specification.  /  is  a  small  pipe 
conveying  the  frothing-agent ;  C  is  a  steam-pipe  ;  b  is  a  Korting  steam- 
jet,  which  allows  the  entrainment  of  a  great  quantity  of  air,  and  d 
is  a  distributer  to  allow  the  air,  steam,  and  oil-vapor  to  be  dissipated 
through  the  pulp.  The  feed-pipe  is  at  g.  The  froth-overflow  is  at  k 
and  the  tailing-discharge  at  m. 

In  the  case  of  an  ore  that  requires  heating,  like  some  sphalerite  ores, 
this  machine  might  be  useful,  because  the  steam  used  for  heating  could 
also  be  made  to  produce  the  aeration.  This  patent  is  assigned  to  Beer, 
Sondheimer  &  Co.,  formerly  agents  for  Minerals  Separation. 

J.  D.  Fields  and  G.  H.  Wyman  have  invented  two  machines  of 
similar  construction.  They  consist  of  a  series  of  flotation  cells,  each 
of  which  has  a  spitzkasten  like  the  M.  S.  standard  machine,  but  in  place 
of  an  impeller  in  an  agitation  compartment  a  jet  of  air  is  used  in  an 
air-lift  for  aerating  and  transferring  the  pulp.  Wyman 's  machine 


MECHANICAL    DEVELOPMENT 


301 


was  invented  several  years  ago  and  was  used  in  several  localities  in 
the  North-West.  The  Fields  machine  grew  out  of  an  'electrolytic'  flota- 
tion-cell that  proved  a  failure.  After  Fields  abandoned  the  use  of  elec- 
tricity in  his  pulp  and  came  down  to  the  use  of  air  for  flotation  he 
obtained  better  results.  The  Keystone  Consolidated  Mining  Co.,  in 
Arizona,  has  used  one  of  these  machines.  The  box,  which  is  divided 
into  small  individual  cells,  is  30  ft.  long,  3  ft.  wide,  and  8  ft.  deep. 


FIG.   33.       GRONDAL   STEAM-JET  MACHINE 

This  is  divided  into  15  cells  each  2  ft.  wide  and  an  air-hose  leads  down 
into  the  bottom  of  each  air-lift.  This  machine  constitutes  the  '  rougher ' 
unit;  a  'cleaner'  unit  of  similar  construction,  but  smaller  size,  is  also 
used.  Nothing  is  known  as  to  the  consumption  of  power,  but  it  is  prob- 
able that  many  of  the  larger  air-bubbles  escape  without  doing  any  use- 
ful work.  If  this  be  true,  this  type  of  machine  could  not  operate  as 
efficiently  as  a  cell  using  a  porous  diaphragm. 

FILM-FLOTATION  MACHINES.  During  recent  years'  not  many  sur- 
face-tension machines  have  been  developed.  The  Wood  machine  and 
the  Macquisten  tube  are  well  known  and  need  not  be  described.  The 
engineers  of  the  New  Jersey  Zinc  Co. — G.  C.  Stone,  A.  R.  Livingston, 
and  L.  G.  Rowand  in  particular — have  invented  various  machines  of 
this  type. 


302  FLOTATION 

Stone's  machine  is  not  shown  here  because  it  does  not  seem  adapted 
to  large-scale  work.  It  consists  of  a  scoop  or  series  of  scoops  fed  with 
dry  crushed  ore  in  a  thin  layer.  The  movement  of  the  scoop  cuts  off 
the  ore-supply  and  it  is  lowered  at  a  slight  angle  into  acidified  water  in 
a  trough.  The  sulphides  float  and  the  gangue  sinks.  The  scoop  reverses 
its  motion  and  passes  back  beneath  the  ore-hopper,  opening  the  ore- 
gate  at  the  bottom  by  properly  arranged  catches.  The  reversal  of  the 
motion  of  the  scoop  closes  the  ore-gate  and  the  scoop  tilts  and  descends 
into  the  water  again.  The  machine  therefore  is  intermittent  in  action 
and  of  complicated  design.  It  is  covered  by  U.  S.  1,156,041  of  October 
5,  1915. 

Livingston's  machine  is  covered  by  U.  S.  patent  1,147,633  of  July 
20, 1915.  Fig.  34  shows  that  it  is  a  much  enlarged  Macquisten  tube,  be- 
ing six  feet  in  diameter  and  about  ten  feet  long.  T^he  ore  is  fed  through 
launder  D.  The  rotation  of  the  drum  carries  the  pulp  up  to  the  left 
and  tacks  or  brads  are  used  to  entrain  more  ore  so  that  it  will  be  lifted 
out  of  the  water  into  the  drum.  A  row  of  water-jets  sprays  the  wall  of 
the  tube  above  the  rising  layer  of  ore,  washing  it  down  and  floating  the 
sulphides  as  a  skin  concentrate  that  overflows  the  side  of  E,  a  launder, 
which  discharges  the  concentrate  outside  the  machine  while  the  tailing 
advances  by  motion  of  the  drum  until  it  falls  into  the  box  C.  The  ad- 
vancing of  the  pulp  from  the  back  end  of  the  drum  to  the  front  is  ac- 
complished by  slanting  plows  placed  on  the  under-side  of  the  concen- 
trate-discharge launder.  The  machine  was  said  not  to  have  been  suc- 
cessful until  the  tacks  were  introduced  for  retaining  the  main  body 
of  ore  while  the  surface  was  being  washed  by  the  descending  jets  of 
water.  The  descending  particles  of  ore  enter  the  water  at  so  slight  an 
angle  and  so  quietly  that  the  sulphides  are  easily  floated.  Aeration 
of  the  incoming  water  is  recommended  and  this  is  accomplished  by 
the  use  of  the  aspirator  h3,  which  sucks  the  air  in  at  h4.  Relatively 
coarse  material,  16  to  20-mesh,  is  said  to  be  best  adapted  for  treatment 
in  this  machine  and  the  patent  specifications  state  that  some  cheap  oil 
and  acid  improve  the  operation.  Data  for  tonnage,  power,  acid,  oil, 
and  labor  are  not  available  but  it  can  be  seen  that  it  is  a  considerable 
improvement  over  the  Macquisten  tube,  being  a  machine  of  much 
larger  capacity.  , 

Rowand's  machine  is  covered  by  U.  S.  1,159,713  of  November  9, 
1915.  A  sketch  of  the  machine,  taken  from  the  patent  specifications, 
is  given  in  Fig.  35.  B  is  the  chute  through  which  powdered  ore,  not 
coarser  than  16-mesh,  is  dropped  in  a  thin  layer  on  a  moving  belt  e 
covered  with  a  film  of  oil.  The  oil  is  stored  in  compartment  /),  into 


MECHANICAL    DEVELOPMENT 


303 


which  the  belt  dips  before  the  ore  is  fed  onto  it.  The  ore  meets  the 
water  at  /  and  the  skin  of  concentrate  is  discharged  over  the  lip,  d, 
into  the  launder  c.  Water  is  fed  through  the  valve  b  and  the  tailing 
discharges  at  a.  Like  Wood's  machine,  the  speed  of  the  belt  deter- 
mines the  movement  of  the  laden  film  on  the  surface  of  the  water.  No 
data  have  been  issued  on  the  speed  of  the  belt  or  the  tonnage. 


F'C.   34.      THE  LIVINGSTON   MACHINE 


304 


FLOTATION 


It  is  possible  that,  as  in  most  skin-flotation  machines,  slime  cannot  be 
treated,  only  fine  sand.  The  oiling  of  the  sulphide  particles  before  en- 
tering the  water  probably  is  done  most  neatly  by  this  arrangement. 

Such  machines  are  not  widely  applicable  because  they  do  not  sep- 
arate slime  cleanly.  They  are  best  adapted  to  the  treatment  of  table- 
middlings  that  consist  of  minerals  of  nearly  the  same  specific  gravity, 
such  as  sphalerite,  barite,  siderite,  fluorite,  and  pyrite. 

GENERAL  CONSIDERATIONS.  Mechanical,  pneumatic,  and  skin-flota- 
tion machines  have  been  considered  separately.  In  many  cases  it  has 
been  found  advantageous  to  use  both  mechanical  and  pneumatic  ma- 
chines in  series  on  the  same  pulp  for  the  reason  that  one  may  do  good 
work  on  the  sand  while  the  other  does  good  work  on  the  slime  constit- 
uent of  the  pulp.  Experience  has  shown  that  it  is  inadvisable  to  com- 


FlG.    35.       THE    ROWAND    MACHINE 


pare  mechanical  with  pneumatic  machines  but  that  they  supplement 
each  other  well.  In  the  order  of  decreasing  coarseness  of  the  pulp  that 
they  will  treat  successfully  we  have  skin,  mechanical,  and  pneumatic 
machines.  There  is  an  apparent  exception  to  this  rule  if  the  flotation 
machine  is  made  to  disperse  the  oil,  as  a  very  'colloidal'  slime  can  then 
be  treated  best  by  a  mechanical  machine  that  gives  intense  agitation. 
If  the  oil  is  fed  into  the  tube-mill  or  other  grinding  machinery  before 
the  pulp  reaches  the  flotation  machines,  no  further  dispersion  is  neces- 
sary and  a  pneumatic  machine  will  show  an  advantage. 


COLLOIDS  305 

COLLOIDS 

By  E.  E.  FREE 

The  following  article  is  made  up  of  portions  of  a  series  of  articles 
on  '  Colloids  in  Ore-dressing, '  which  appeared  in  the  Engineering  and 
Mining  Journal  during  19 16.1  It  is  a  pleasure  to  express  my  thanks 
to  the  editor  of  that  journal  for  permission  to  use  the  material  in  this 
place.  The  alterations  from  the  original  text  are  almost  entirely  by 
way  of  condensation. 

The  conceptions  of  colloids  to  be  found  in  the  current  literature  of 
ore-dressing  are  surprisingly  hazy.  With  increasing  interest  in  the 
flotation  processes  the  catchwords  of  two  years  ago  have  given  way  to  a 
new  set  of  phrases  involving  '  surface  forces, '  '  interf acial  tensions, '  and 
the  like.  The  relief  to  the  overworked  ' colloids'  is  considerable  and 
one  is  grateful  for  the  lessened  tendency  to  ' explain'  obscure  phenom- 
ena by  reference  to  mysterious  'colloidal  substances'  that,  themselves 
remaining  unknown,  leave  the  problem  precisely  where  it  was  before. 
This  lessened  misuse  of  colloidal  concepts  appears  to  be  accompanied — 
one  may  hope  that  it  is  caused — by  a  more  definite  appreciation  of  the 
physical  and  chemical  nature  of  colloidal  bodies,  an  appreciation  that 
may  be  expected  to  bring  important  returns  in  actual  experimenta- 
tion, advancing  our  knowledge  of  these  bodies  and  of  their  metallur- 
gical significance. 

In  the  original  text  of  these  papers  considerable  attention  was  de- 
voted to  the  loose  use  of  colloidal  terminology  caused  by  a  compari- 
son between  the  kinds  of  colloids  present  in  ore-slimes  and  the  glue- 
like  bodies,  also  called  'colloids,'  of  which  gelatine  and  albumen  are 
typical.  It  was  pointed  out  that  there  are  important  differences  be- 
tween these  glue-like  bodies  and  the  materials  encountered  in  metal- 
lurgical practice  and  that  the  examination  of  the  latter  is  best  ap- 
proached by  abandoning  all  preconceptions  concerning  the  gelatin- 
ous colloids  and  by  confining  attention,  in  the  beginning  at  least,  to 
the  properties  of  simple  rock-powders.  So  far  as  is  actually  known 
ore-slimes  consist  merely  of  fine  mineral  particles  suspended  in 
water  that  usually  contains  dissolved  traces  of  the  minerals  present 
in  the  ore.  It  was  asserted  that  the  determinable  properties  of 
such  a  simple  suspension  of  rock-particles  in  water  would  explain 


.  cG  Min.  Jour.,  Vol.  101,  pp.  249-254,  429-432,  509-513,  681-686,  1068-1070, 
1105-1108  (February  to  June,  1916). 


306  FLOTATION 

the  behavior  of  slimes,  even  the  most  colloidal  ones,  without  need  of 
assuming  the  presence  of  gelatinous  substances  or  other  intangible 
mysteries.  It  is  obvious  that  the  physical  properties  of  simple  sus- 
pensions become  of  much  importance  to  the  inquiry. 

Fortunately,  suspensions  have  been  studied  thoroughly"  by  geol- 
ogists, soil-physicists,  and  the  specialists  in  colloids.  The  most 
weighty  result  of  this  study  is  the  conception  of  the  possible  exist- 
ence of  suspensions  of  smaller  and  smaller  particles.2  It  is  possible 
to  prepare  suspensions  of  clay  or  other  minerals  the  particles  of 
which  are  so  fine  that  they  remain  permanently  suspended,  though 
still  distinguishable  by  microscopic  examination.  It  is  a  small  step 
from  this  to  the  typical  colloidal  solutions  that  appear  free  of  par- 
ticles ("optically  empty")  before  the  microscope.  The  investigations 
of  colloidal  solutions  made  possible  by  the  ultramicroscope,3  during 
the  past  decade,  have  established  firmly  the  conclusion  that  the  typ- 
ical colloidal  solution,  as,  for  instance,  that  of  colloidal  gold,  is  sim- 
ply a  suspension  in  which  the  particles  are  extraordinarily  small. 

The  important  concept  here  is  the  perfect  continuity  of  the  sus- 
pension series.  There  is  no  natural  break  or  division  of  any  kind 
between  a  suspension  of  coarse  gold  fragments  in  water  and  a  col- 
loidal solution  of  gold  particles  so  fine  as  to  remain  permanently 
suspended  and  be  microscopically  invisible.  It  is  possible  to  prepare 
a  suspension  of  any  intermediate  degree  of  fineness.  Indeed,  if  one 
regards  ordinary  solutions  as  composed  of  single  molecules  or  ions 
distributed  through  the  mass  of  the  solvent,  these  'true'  solutions 
appear  simply  as  the  limiting  case  of  the  suspension  series — suspen- 
sions in  which  the  particles  have  become  so  small  as  to  reach  the  di- 
mensions of  the  molecule  or  the  ion. 

The  immediately  obvious  objection  to  this  concept  of  the  unity  of 
the  suspension  series  from  the  coarse  visible  suspension  at  one  end 
to  the  true  solution  at  the  other,  is  that  the  properties  of  the  systems 
differ  markedly  in  different  parts  of  the  series.  A  mixture  of  coarse 
gold  particles  and  water  is  very  different  physically  from  a  colloidal 
gold  solution,  and  both  differ  in  properties  from  a  solution  oP,  say, 
gold  chloride  containing  the  gold  ion.  This  is  quite  true,  but  close 
examination  of  the  series  shows  that  all  differences  are  of  degree 


2For  details  see  Ashley,  U.  S.  Geological  Survey,  Bull.  388  (1909)  and 
Bureau  of  Standards,  Technologic  Paper  23  (1911),  and  the  general  works 
cited  in  the  appended  bibliography. 

sSiedentopf  &  Zsigmondy,  Ann.  Physik,  Ser.  4,  Vol.  10,  pp.  1-39  (1903). 
In  English  see  Zsigmondy,  'Colloids  and  the  Ultramicroscope,'  translated  by 
Alexander,  1909. 


COLLOIDS  307 

only.  Thus,  in  a  coarse-sand  suspension,  the  most  evident  controll- 
ing factor  is  gravity.  Nothing  but  the  continuous  expenditure  of 
energy  (for  example  by  shaking)  will  keep  the  sand  suspended.  As 
we  consider  suspensions  of  finer  particles,  gravity  grows  less  and 
less  important,  while  simultaneously  the  surficial  forces  between  the 
particles  and  the  aqueous  medium  grow  more  and  more  important 
until  gravity  yields  control  to  these  other  forces  and  the  particles  re- 
main in  permanent  suspension  without  external  assistance.  This 
is  typical.  The  changes  are  always  gradual  as  one  passes  up  or 
down  the  series;  they  always  result  from  continuous  increases  or  de- 
creases in  the  intensity  of  the  affecting  factors.  They  are  never 
abrupt.  From  the  practical  viewpoint,  however,  it  is  precisely  these 
gradual  changes  of  degree  that  are  important.  The  fact  that  the 
properties  of  the  finer-grained  suspensions  do  differ  from  those  of 
the  coarser  is  what  has  attracted  attention.  It  is  important  theoret- 
ically to  know  that  the  differences  are  of  degree  rather  than  kind, 
but  that  does  not  dispose  of  the  differences. 

The  most  troublesome  properties  of  colloidal  ores  are  two, 
namely,  the  slow  settling  of  slime,  which  also  means  the  imperfect  sep- 
aration between  fine  and  coarse  particles,  and  the  low  permeability 
of  settled  masses  of  slime,  filter-cakes,  and  the  like.  The  latter  is 
usually  accompanied  by  a  high  retention  of  water  in  the  thickened 
slimes.  Both  of  these  are  comparative  rather  than  absolute.  The  col- 
loidal slime  settles  slowly  and  packs  imperviously  by  comparison  with 
slime  th£t  is  less  colloidal.  It  is  easy  to  demonstrate  by  experiment 
with  suspensions  of  known  character  that  slowness  of  settling  and 
the  other  troublesome  properties  increase  gradually  and  continu- 
ously with  decrease  of  the  particle,  and  it  is  an  obvious  inference 
that  an  unusually  small  size  of  particle  is  the  cause  of  all  the  trouble 
with  colloidal  slimes.  The  mechanisms  may  be  pictured  by  recall- 
ing that  in  dilute  suspensions  gravity  becomes  less  important  and 
surficial  forces  more  important  as  the  particles  decrease  in  size,  and 
that  in  thickened  masses  of  slime,  if  the  particles  are  very  small,  the 
spaces  between  the  particles  are  similarly  tiny  and  offer  tremen- 
dous frictional  resistance  to  the  percolation  of  water. 

These  effects  of  minute  particles  are  so  manifest  and  so  mani- 
festly sufficient  to  explain  the  behavior  of  slime  that  I  suspect  no 
other  explanation  would  have  been  suggested  were  it  not  for  the  an- 
omalous fact  that  the  degree  of  colloidality  of  a  slime  has  no  con- 
stant or  determinable  relation  to  the  fineness  of  grinding  of  the  ore 
or  to  the  amount  of  very  fine  material  in  the  slime  as  determined  by 


308  FLOTATION 

screen-tests,  by  elutriation,  or  by  other  methods.  There  is  much 
more  likely  to  be  a  relation  to  the  original  character  of  the  ore.  For 
instance,  oxidized  and  'rotten'  ores  are  especially  prone  to  yield 
colloidal  slimes.  These  anomalies  are  to  be  explained  by  two 
things :  the  variable  disintegration  of  ores  and  the  variable  floccula- 
tion  of  the  slimes.  The  ease  of  disintegration  is  essentially  a  matter 
of  mineral  composition.  Mechanical  grinding  by  itself  cannot  re- 
duce ore-particles  beyond  a  certain  size,  which  is  probably  consid- 
erably above  the  size  necessary  for  high  colloidality.  If  disintegra- 
tion occurs  beyond  this  limit  of  mechanical  grinding,  it  is  because 
the  ore  or  some  of  its  constituents  are  of  such  physical  nature  as  to 
disintegrate  spontaneously  when  shaken  with  water,  as,  for  instance, 
clay  will  disintegrate.  Natural  processes  of  weathering  in  the  ox- 
idation zone  tend  to  produce  materials  that  will  so  disintegrate,  as, 
for  instance,  when  feldspar  is  altered  to  kaolin.  By  the  second 
factor,  flocculation,  is  meant  the  aggregation  of  several  smaller  par- 
ticles into  more  or  less  persistent  groups  or  floccules,  which  then 
behave  much  like  single  larger  particles.  This  will  be  discussed  in 
detail  below. 

The  most  important  result  of  the  study  of  colloids  and  suspen- 
sions during  the  past  decade  is  the  conception  of  colloids  simply  as 
suspensions  the  particles  of  which  are  very  small.4  It  is  unneces- 
sary to  nmke  any  sharp  distinction  between  suspensions  and  col- 
loidal solutions.  The  emphasis,  indeed,  is  reversed  and  is  on  the 
unity  of  this  series  rather  than  on  any  possible  severalty  *  but  for 
the  purposes  of  purer  science  it  is  convenient  to  have  distinctions, 
so  that  a  greater  precision  of  definition  becomes  necessary.  For 
these  purposes  there  has  come  to  be  nearly  general  agreement  on  a 
set  of  size-limits  given  in  the  following  table  :5 

CLASSIFICATION  BY  SIZE  OF  PARTICLES 

Suspensions Particles  over  0.1      micron  in  mean  diameter 

Colloidal  solutions. .  .Particles  between  0.1  and  0.001  micron  in  mean  diameter 
True  solutions..  ..Particles  under  0.001  micron  in  mean  diameter 


4The  detailed  experimental  evidence  supporting  this  conclusion  is  ample 
and  beyond  question,  but  its  discussion  would  require  too  much  space.  It 
will  be  found  in  detail  in  the  works  of  Freundlich,  Ostwald,  and  Zsigmondy, 
cited  in  the  appended  bibliography.  It  is  excellently  summarized  by  John 
Johnstone  in  his  introduction  to  Ashley's  monograph  on  the  'Technical  Con- 
trol of  the  Colloidal  Matter  of  Clays,'  U.  S.  Bureau  of  Standards,  Technologic 
Paper  23  (1913). 

sZsigmondy,  'Erkenntniss  der  Kolloide,'  p.  22  (1905).  A  micron  is  one- 
thousandth  of  a  millimetre,  or  approximately  one  twenty-thousandth  of  an 
inch.  \ 


COLLOIDS  309 

While  these  limits  are  purely  arbitrary,  the  use  of  them  is  con- 
venient as  indicating  the  range  of  size  within  which  the  typical  col- 
loidal properties  are  best  developed.  It  is  not  implied  that  these 
properties  cease  entirely  to  be  exhibited  by  suspensions  the  particles 
of  which  lie  outside  these  limits.  In  metallurgy  especially  it  is  nec- 
essary to  consider  many  important  extensions  of  colloidal  properties 
into  the  field  of  the  coarser  suspensions.  Nearly  all  slimes,  even 
the  most  colloidal,  belong  to  the  field  of  suspensions  rather  than  to 
that  of  colloidal  solutions,  as  these  fields  are  defined  by  the  size-lim- 
its given. 

This  conception  of  colloids  points  immediately  at  the  chief  char- 
acteristic of  these  bodies  and  the  one  that  is  at  the  bottom  of  most 
of  their  properties,  namely,  their  great  internal  surface.  It  is  man- 
ifest that  if  a  colloid  is  composed  of  very  fine  particles  of  one  sub- 
stance suspended  in  another,  the  total  surface  of  contact  between 
the  two  substances  will  be  very  great.  This  mutual  surface  is  called 
the  internal  surface.  It  has  been  found  that  a  number  of  peculiar 
properties,  of  which  surface-tension  is  the  best-known,  characterize 
all  surfaces  where  two  substances  come  into  contact,  and  the  great 
extent  of  such  surface  in  suspensions  and  colloids  gives  these  sur- 
ficial  properties  and  forces  an  unusual  importance  in  controlling  the 
salient  characteristics  of  the  entire  system.  For  instance,  the  phe- 
nomena of  adsorption  or  the  concentration  of  dissolved  substances 
at  surfaces  are  exhibited  in  a  high  degree  by  suspensions  and  col- 
loids and  are  of  much  technical  importance  in  dyeing,  the  clari- 
fication of  wines,  the  manufacture  of  contact  sulphuric  acid,  and  in 
many  other  industrial  processes. 

In  speaking  of  the  large  internal  surface  of  colloids  one  means, 
of  course,  that  the  surface  is  relatively  extensive  with  respect  to  the 
masses  involved.  The  criterion  is  a  large  ratio  of  internal  surface 
to  mass.  Formal  definitions  are  of  small  value,  but  it  is  possible 
to  define  a  colloid  from  this  viewpoint  as  a  mixture,  of  at  least  two 
substances  the  internal  surface  of  which  is  very  large  relative  to  the 
mass  of  at  least  one  of  the  substances.  It  may  be  pointed  out  again 
that  the  definition  is  purely  relative.  What  ratio  of  surface  to 
mass  is  to  be  considered  'very  large'  will  depend  upon  circum- 
stances. 

In  the  foregoing  paragraphs  there  has  been  much  mention  of 
colloidal  properties,  but  the  only  ones  that  have  been  discussed  spe- 
cifically are  the  slow  settling  of  colloidal  slimes  and  their  impervi- 
ousness  when  settled.  From  the  standpoint  of  ore-dressing  these 


310  FLOTATION 

two  are  the  most  important  of  all  colloidal  properties,  and  the  em- 
phasis is  not  unjustified.  However,  several  other  properties  are  of 
interest.  Most  important  scientically  are  the  similiarities  to,  and 
differences  from,  the  true  or  ordinary  solutions  the  particles  of 
which  are  supposed  to  be  of  molecular  or  ionic  dimensions.  The 
typical  colloidal  solution  resembles  a  true  solution  in  being  persist- 
ent so  long  as  conditions  remain  unchanged.  That  is.  the  particles 
remain  in  suspension  arid  the  colloidal  solution  retains  an  un- 
changed chemical  composition.  The  colloids  differ  in  (1)  failure  to 
show  a  true  and  constant  solubility;  (2)  an  optical  heterogeneity 
shown  by  translucence  or  turbidity;  (3)  the  causing  of  no  change, 
or  a  very  small  change,  in  the  freezing-point  and  boiling-point  of 
the  solvent;  (4)  the  production  of  no  osmotic  pressure;  (5)  slow 
diffusion  and  failure  to  dialyze  or  pass  through  a  parchment  mem- 
brane. The  causes  of  all  these  differences  will  be  evident  on  consid- 
eration of  the  difference  in  particle-size  that  distinguishes  the  col- 
loids from  the  true  solutions.  Details  need  not  be  pursued  further 
than  to  say  that  the  differences,  as  before,  are  of  degree  only.  Col- 
loids do  not  fail  entirely  to  show  the  typical  solution  properties,  but 
they  show  them  to  so  slight  a  degree  as  to  escape  all  but  the  most 
painstaking  researches. 

Of  the  other  properties  of  colloids,  flocculation  and  adsorption 
have  been  mentioned  and  will  be  discussed  further  below.  Another, 
of  much  technical  importance,  is  the  tendency  of  the  colloidal  par- 
ticles to  wander  in  the  electric  field  and  accumulate  at  one  or  the 
other  of  the  poles.  This  forms  the  basis  of  the  well-known  Cottrell 
process  for  the  collection  of  acid  and  smelter-fume,  the  removal  of 
dust  from  stack-gases,  the  separation  of  oil-globules  from  condenser- 
water,  and  the  like. 

In  what  precedes,  the  reader  has  probably  detected  a  tacit  assump- 
tion that  all  colloids  consist  of  solid  particles  suspended  in  a  liquid 
medium.  It  is  easiest  to  attain  an  initial  concept  of  the  nature  of 
colloids  by  regarding  them  in  this  wray,  but  the  concept  is  incom- 
plete. Common  experience  furnishes  numerous  examples  outside 
this  simple  case.  For  instance,  the  usual  medicinal  emulsions  of 
cod-liver  oil,  or,  to  use  an  illustration  with  pleasanter  associations, 
the  ordinary  oil-vinegar  salad  dressing,  consists  of  globules  of  oil 
suspended  in  an  aqueous  liquid.  Obviously  both  particle  and  med- 
ium are  liquid,  yet  the  properties  of  the  mixture  are  (with  some 
exceptions  in  detail)  the  typical  colloidal  properties.  As  a  matter  of 
fact  it  is  possible  to  prepare  suspensions  and  colloidal  mixtures  the 


COLLOIDS 


311 


particles  of  which  are  solid,  liquid,  or  gaseous,  and  which  are  sus- 
pended either  in  solid,  liquid,  or  gaseous  media.  In  1907  Ostwald6 
published  a  classification  on  this  basis,  which  classification  is  given 
below  in  tabular  form  and  supplied,  so  far  as  possible,  with  metal- 
lurgical examples.  In  selecting  the  examples  no  attempt  has  been 
made  to  distinguish  between  colloidal  solutions  and  the  coarser  sus- 
pensions. It  is  obvious  also  that  examples  of  all  of  these  classes  ex- 
ist among  the  true  solutions. 


Solid   medium 


A  CLASSIFICATION   OF  COLLOIDS 
Liquid  medium 


Gaseous    medium 


Stl 


Many  cryptoorystalline  ores,     Ordinary     suspensions     and    Fume   and   smoke. 


especially   those  contain- 
ing:  finely  divided  metals. 

Most  solidified  slag's. 

Glazes,    g-lasses,   etc. 


Flue-dust. 


colloidal      solutions      of 

solid  particles. 

Slimes,    thickened    or    not.     ?*&&£?>&  floui"mills- 
Wet    plastic   clays. 
Turbidity  in   water. 


factories,    etc. 
Systems    involved    in    proc- 
esses   of    air    separation. 


_  jj    Liquid    inclusions    in    crys-     Emulsions.  Fog,  cloud,  and  wet  steam. 

'IS        tals-  Oil  in  condenser-water  and    Acid-fume.       Collection    of 

£•"£    Much    occluded    water    and          water  in   fuel-oil.  acid   from   smelters,    fer- 

tilizer-works,  etc. 


2         water   of   crystallization.     The    g.iue.like    organic    col- 


Some       filter-cakes, 
while  wet. 


etc.,          loids. 


Dry  filter-cakes. 
s.2    Silica-brick        and 
§;-         other  refractories. 
s  B    Mineral-wool 
&  n        sponge. 


Foams  and  froths, 
many     Wet  steam    (phenomena  of 

foaming   in    boilers). 

and      metal-     Systems    used    in    gas    and 
foam    processes    of    ore- 


Oil-sprays. 


No  tangible  examples. 


Gas-inclusions  in  crystals. 


separation. 


Of  course,  the  limit  of  colloidal  complexity  is  not  reached  by  the 
examples  in  the  table.  Only  two  substances  are  there  considered, 
the  particle  and  the  medium.  The  medium  is  regarded  as  homogene- 
ous, and  all  particles  are  assumed  to  be  of  the  same  substance.  It  is 
obviously  possible  to  have  more  than  one  kind  of  particle  or  a  med- 
ium that  is  itself  complex,  and  it  is  not  necessary  for  all  of  the  par- 
ticles to  be  solid,  or  liquid,  or  of  any  single  state. 

The  particulate  theory  of  colloids  and  the  classification  accord- 
ing to  the  respective  physical  states  of  the  phases  is  reflected  in  the 
terminology  developed  for  the  subject.  Thus  a  useful  concept  re- 
gards the  size  of  particle  as  due  to  the  'degree  of  dispersion'  of  the 
particulate  substance.  A  decreased  size  of  particle  is  spoken  of  as  a 
greater  'dispersion,'  or  the  substance  as  more  highly  'dispersed.'  By 
extension  all  suspensions  and  colloids  are  'disperse'  (or  'dispersed') 
systems  or  ' dispersoids ; '  the  particles  compose  the  'disperse'  phase 
and  the  medium  is  the  'dispersion  medium.'  A  true  solution  pos- 


«Grundriss  der  Kolloidchemie,'  first  edition,  pp.  94-7  (1907).     English,  edi- 
tion, pp.  42-43. 


312  FLOTATION 

sesses  a  molecular  or  ionic  degree  of  dispersion  and  is  a  'mol'  or 
'ion-dispersoid.'7  These  terms  include  all  colloidal  systems,  re- 
gardless of  the  solid,  liquid,  or  gaseous  state  of  particle  or  medium. 
Colloidal  solutions  with  a  liquid  medium  are  referred  to  as  'sols.' 
If  the  medium  is  water,  the  colloid  is  a  'hydrosol;'  if  alcohol,  an 
'  alcoholsol, '  or  'alcosol,'  etc.  By  analogy  with  the  systems  of 
coarser  particles  the  solid-particle  sols  are  frequently  called  'sus- 
pensoids;' those  of  liquid  particles,  'emulsoids.'  The  terms  'sol,' 
*  suspensoid, '  and  'emulsoid,'  with  their  compounds,  are  properly 
applied  only  to  systems  within  the  assigned  colloidal  range  of  parti- 
cle size. 

The  distinction  between  emulsoids  and  suspensoids  on  the 
basis  of  the  liquid  or  solid  character  of  suspended  particles  has 
been  generally  accepted,  but  recent  evidence  indicates  that  this  is 
not  precisely  the  ground  of  difference  between  typical  members  of 
the  two  classes.  The  typical  emulsoids  are  gelatine  and  the  related 
glue-like  colloids.  The  typical  suspensoids  are  the  colloidal  solu- 
tions of  metals.  These  classes  differ  markedly  in  many  properties ; 
for  instance,  the  metal  sols  are  much  more  easily  precipitated  by 
electrolytes.  However,  a  suspension  of  small  droplets  of  mineral- 
oil  in  water  behaves  much  more  like  the  metal  sols  than  like  the  typ- 
ical emulsoids  such  as  gelatine.  It  is  probable  that  the  explanation 
lies  in  two  facts.  First,  the  globules  of  oil  are  so  small  that  they 
are  practically  rigid  and  behave  like  solid  particles.  Second,  the 
materials  of  the  typical  glue-like  emulsoids  are  miscible  with  water. 
Thus  the  gelatine  sol  has  been  shown  to  consist  of  two  phases  both 
of  which  are  solutions  of  gelatine  in  water.8  The  globules  are  com- 
posed of  a  concentrated  solution  of  gelatine  and  are  in  a  medium 
that  is  a  dilute  solution  of  gelatine.  Under  proper  circumstances 
water  can  pass  from  globule  to  medium  or  the  reverse,  resulting  in 
changes  of  the  gelatine  concentrations  in  the  two  phases  and  in 
shrinkage  or  swelling  of  the  globule  phase.  It  is  believed  that  this 
behavior  is  responsible  for  the  peculiar  properties  of  the  glue-like 
colloids  and  it  is  probable  that  we  must  recognize  two  classes  of 
emulsoids,  as  that  term  is  above  defined.  One  class  will  consist  of 
those  liquid-particle  colloids  the  particles  of  which  cannot  absorb 
the  medium,  like,  for  instance,  mineral-oil  in  water.  The  other  class 


?This  terminology  is  due  to  Wo.  Ostwald,  Roll.  Zeits.,  Vol.  I.  pp.  291-300, 
331-41  (1907);  'Grundriss  der  Kolloidchemie,'  1st  ed.,  p.  83  (1909);  English 
ed.,  p.  24. 

sHatschek,  'introduction  to  the  Physics  and  Chemistry  of  Colloids,'  p.  46 
(1913). 


COLLOIDS  313 

will  contain  those  in  which  water  can  be  absorbed  by  the  particle. 
These  will  include  gelatine  and  its  analogues. 

It  is  the  emulsoids  of  this  second  class  that  form  the  'gels;'  jel- 
lies of  the  sort  typified  by  the  ordinary  table  jellies  made  from  gel- 
atine or  the  pectin  of  fruit-juices.  The  discussion  of  the  structure 
and  properties  of  gels  would  take  us  far  afield.  It  may  be  noted, 
however,  that  the  only  inorganic  gel  of  common  occurrence  is  that 
of  silicic  acid  or  hydrated  silica.  The  effect  of  the  gel-forming  emul- 
soids on  the  flocculation  of  suspensions  will  be  noted  below  and  we 
shall  then  return  briefly  to  the  possiblity  of  their  occurrence  in  ores 
and  slimes. 

From  the  practical  point  of  view,  in  ore-dressing  at  least,  the 
most  important  properties  of  colloids  and  other  suspensions  are 
those  that  are  concerned  with  the  rate  of  subsidence  of  the  particles 
through  the  medium.  This  is  what  controls  the  rate  of  settling  of 
slimes  and  the  many  practical  matters  depending  thereon.  When  a 
single  mineral  particle  falls  freely  through  water  or  any  fluid  med- 
ium it  soon  attains  (if  it  be  not  too  large)  a  constant  velocity,  which 
is  maintained  thereafter  regardless  of  the  distance  it  falls.  This 
constant,  velocity  is  expressed  mathematically  by  a  formula  due  to 
Stokes,9  as  follows: 


in  which  v  is  the  velocity,  r  is  the  radius  of  the  particle,  d  and  dl 
are  the  densities  of  the  particle  and  medium  respectively,  g  is  the 
acceleration  of  gravity,  and  k  is  a  constant  depending  upon  the  vis- 
cosity of  the  solution. 

Ignoring  the  self-evident  effects  of  gravity  and  of  the  difference 
in  densities,  it  is  apparent  that  the  velocity  of  fall  of  a  particle  will 
vary  directly  with  the  square  of  its  radius  and  inversely  with  the 
viscosity  of  the  medium  through  which  it  falls.  The  chief  depar- 
tures from  this  formula  that  are  encountered  in  experiment  occur 
with  the  smaller  particles,  these  falling  more  slowly  than  is  required 
by  the  theory.  It  is  probable  that  such  deviations  are  due  to  several 
forces,  active  only  in  the  case  of  the  finer  particles  and  not  taken 
into  account  in  the  formula,  of  which  forces  the  chief  appear  to  be 
molecular  bombardment  and  electric  charges  on  the  particles.  The 
possible  efficacy  of  repulsive  electric  charges  in  modifying  the  rato 


"Trans.  Camb.  Phil.  Soc.,  Vol.  9,  Part  2,  pp.  51-2  (1850).  For  more  recent 
treatments  see  Cunningham,  Proc.  Roy.  Soc.  (London),  Ser.  A,  Vol.  83,  pp. 
357-65  (1910)  ana  Lamb,  Phil  Mag.,  Ser,  6,  Vol.  21,  pp.  112-21  (1911). 


314  FLOTATION 

of  fall  is  obvious.  Knowledge  of  the  importance  of  molecular  bom- 
bardment is  due  to  recent  work  demonstrating  that  the  vibratory 
movement  of  suspended  particles  known  as  the  Brownian  movement 
is  really  due  to  bombardment  of  the  particles  by  the  moving  mole- 
cules of,  or  in,  the  medium.10  It  follows  that  small  suspended  parti- 
cles have  in  some  degree  a  tendency  to  become  distributed  through- 
out the  medium,  a  tendency  similar  in  kind  to  the  diffusiveness  of 
a  gas  or  of  a  dissolved  substance,  but  much  less  intense.  In  actual  ex- 
periment, furthermore,  we  seldom  deal  with  a  medium  entirely 
free  from  convection  currents  and  even  less  often  with  particles  that 
are  perfect  spheres.  Any  such  disturbances  in  the  medium  or  irreg- 
ularities in  shape  of  the  particle  will  retard  settling,  and  it  is  ob- 
vious that  the  rates  of  fall  actually  found  may  be  importantly  below 
those  expected  on  the  basis  of  the  formula.  All  of  these  disturbing 
factors  lead  to  decreases  rather  than  increases  in  the  rate  of  settling 
required  by  the  formula,  which  it  is  possible  to  regard  as  an  expres- 
sion of  the  limiting  maximum  velocity  that  a  given  particle  can  at- 
tain in  a  given  medium.  The  actual  velocity  will  be  always  smaller 
than  the  theoretical. 

From  the  presence  in  the  formula  of  the  square  of  the  radius 
of  the  particle  it  follows  that  the  velocity  of  fall  decreases  rapidly 
with  decrease  in  size.  In  this  a-nd  in  the  fact  that  all  devia- 
tions are  toward  lesser  rather  than  greater  rates  lies  the  cause  of 
the  extremely  slow  rates  of  subsidence  exhibited  by  fine  clays,  slimes, 
and  the  like.  Indeed,  with  ordinary  mineral  particles  in  an  aqueous 
medium  and  under  the  usual  conditions  of  experiment  or  of  metal- 
lurgical practice,  single  particles  entirely  cease  to  subside,  although 
large  enough  to  be  microscopically  visible  and  considerably  larger 
than  the  diameter  established  by  the  Zsigmondy  table  as  the  upper 
limit  of  truly  colloidal  particles.  This  means  that  suspensions  that 
are  not  fine-grained  enough  to  be  colloids  at  all,  in  the  technical 
sense  of  the  word,  are  capable  of  persistent  suspension  and  that 
much  of  the  material  of  many  slimes  would  not  settle  at  all  were  it 
controlled  only  by  the  factors  mentioned.  The  fact  that  slimes  do 
settle  and  that  the  situation  is  not  so  bad  as  would  be  inferred 
from  the  theory  outlined  brings  us  to  the  matter  of  flocculation. 

Flocculation  is  the  technical  term  for  the  gathering  of  suspended 
particles  into  aggregates.  An  aggregate  composed  of  many  parti- 


i°For  a  review  of  this  subject,  with  citations  of  literature  see  Wo.  Ostwald, 
'Grundriss  der  Kolloidchemie,'  2nd  ed.,  pp.  231-61  (1911);  English  ed.  pp. 
186-210. 


COLLOIDS  315 

cles  will  behave  to  some  degree  like  a  single  larger  particle,  although 
one  of  very  irregular  surface.  It  follows  that  flocculation  changes 
the  suspension  from  one  of  a  multitude  of  tiny  particles  into  one 
that  behaves  as  though  it  were  composed  of  a  relatively  small  num- 
ber of  larger  particles.  The  average  effective  radius  of  particle  is 
increased,  and  the  Stokes  formula  indicates  the  increase  to  be  ex- 
pected in  the  rate  of  settling,  it  being  remembered  that  this  increase 
will  correspond  to  the  squares  of  the  respective  radii.  Experiment 
is  fully  confirmatory.  A  flocculated  clay-suspension  will  subside  in 
a  few  minutes  whereas  the  same  material,  unflocculated,  may  re- 
main suspended  indefinitely.  The  rate  of  settling  may  be  largely  in- 
creased, even  multiplied  by  hundreds  or  thousands,  by  flocculation, 
and  in  this  lies  the  explanation  of  much  of  the  anomalous  behavior 
of  colloidal  slimes.  Slimes  settle  faster  or  more  slowly  not  only  in 
response  to  the  actual  size  of  the  ultimate  mineral  particles,  but 
also  in  response  to  the  more  or  less  complete  flocculation  of  these 
ultimate  particles  into  larger  or  smaller  aggregates.  These  floccules 
are  not  fixed  enough  to  persist  through  screen-testing  or  elutriation 
even  when  it  can  be  carried  to  their  dimensions,  and  the  reason  for 
the  failure  of  such  tests  to  agree  with  the  degree  of  colloidality  en- 
countered in  practice  is  clear. 

It  should  be  noted  that  flocculation  and  its  opposite,  defloccula- 
tion,  are  purely  relative  terms  like,  for  instance,  'high'  and  'low' 
or  'smoothness'  and  'roughness.'  A  suspension  is  more  or  less  floc- 
culated merely  with  reference  to  some  other  suspension.  For  this 
reason  it  is  preferable  to  use  the  concept  of  'degree  of  flocculation' 
rather  than  to  refer  to  suspensions  as  'flocculated'  or  ' deflocculated. ' 
Precision  in  the  determination  of  this  degree  of  flocculation  is  not  yet 
possible.  No  method  is  known  for  the  accurate  measurement  of  floc- 
cules or  the  counting  of  their  constituent  particles,  and  even  if  there 
were,  it  is  probable  that  the  individual  floccules.  of  a  single  suspension 
would  vary  widely  and  irregularly  among  themselves. 

The  degree  of  flocculation  of  a  suspension  is  extremely  sensitive 
to  surrounding  conditions;  so  sensitive,  indeed,  that  changes  of  floc- 
culation in  the  true  colloidal  solutions  are  among  the  most  delicate 
of  analytical  reactions.  These  changes  and  similar  ones  in  the 
coarser  suspensions  may  be  caused  by  many  kinds  of  influences. 
Temperature,  light,  the  radiations  from  radium,  electro-static 
charges,  and  many  other  variations  in  energy  relations  all  appear  to 
have  perceptible  effects.  However,  these  effects  of  direct  energy  are 
less  important  than  the  effects  of  added  substances,  and  it  is  these 


316 


FLOTATION 


latter  alone  that  require  consideration  here.  A  large  amount  of  ob- 
servation and  incidental  experiment  going  back  for  centuries  has 
established  three  general  classes  of  substances  that  effect  the  degree 
of  flocculation  or,  as  it  is  generally  conceived,  the  rate  of  settling 
of  suspensions.  First  are  the  neutral  inorganic  salts  and  the  inor- 
ganic acids,  all  of  which  increase  the  degree  of  flocculation  and  pro- 
mote settling.  Second  are  the  alkalies  which  (in  certain  concentra- 
tions) have  the  reverse  effect;  they  decrease  the  degree  of  flocculation 
and  hinder  settling.  These  are  known  as  'deflocculators/  Third  are 
the  gel-forming  emulsoids,  such  as  gelatin  and  the  like.  The  effect 
of  these  is  somewhat  complex,  but  in  general  they  also  decrease  the 
degree  of  flocculation,  or  at  least  prevent  its  increase. 

A  convenient  illustration  of  the  effect  of  a  flocculating  agent  is 
furnished  by  a  series  of  measurements  of  the  flocculating  effect  of 
sodium  chloride  upon  kaolin  suspensions  recently  made  by  Herbert 
F.  McCall  under  my  direction.  The  data  are  shown  graphically  in  Fig. 


t 
o 

0 

D 

u 

t 

5) 

a 

ooc 

„ 

/ 

/ 

• 

10?  0.005     0.05  0. 

0     0.25                 1.00                  3.00             5.00           8.0 

FIG.  1 

1,  the  degree  of  flocculation  being  expressed  upon  the  vertical  axis, 
the  concentration  of  sodium  chloride  upon  the  horizontal.  For  con- 
venience the  scale  of  the  horizontal  axis  is  cubed.  The  degree  of 
flocculation  cannot  be  set  down  in  any  absolute  or  standard 
units.  The  curve  expresses  no  more  than  the  relative  degree  of 
flocculation  of  suspensions  in  solutions  of  different  concentration 
and  has,  so  far  as  its  vertical  dimension  is  concerned,  only  a  roughly 
quantitative  value.  From  this  curve  it  is  apparent  that  in  extremely 
dilute  solutions  there  is  no  perceptible^  effect  on  the  degree  of  floe- 


COLLOIDS  317 

filiation.  At  a  concentration  of  about  0.0005  gramme  per  litre  an 
increased  flocculation  begins  to  be  perceptible;  this  increases  rather 
rapidly  at  first  and  then  more  slowly  to  a  maximum  at  about  0.07 
gm.  per  litre,  beyond  which  increases  of  concentration  produce  no 
further  perceptible  effect  on  the  degree  of  flocculation.  The  experi- 
ments were  extended  to  saturation  (250  gm.  per  litre),  but  the  cor- 
responding portion  of  the  curve  is  not  shown  in  the  figure. 

This  behavior  is  characteristic  of  nearly  all  soluble  salts  and 
acids  acting  on  most  suspended  substances.  The  initial  concentra- 
tion at  which  an  effect  begins  to  be  apparent  is  known  as  the  'thresh- 
hold  concentration,'  and  varies  considerably  in  suspensions  of  differ- 
ent materials  and  with  different  salts  or  acids.  It  is  worth  noting 
that,  contrary  to  the  current  conception  of  the  matter,  this  thresh- 
hold  concentration  is  not  a  sharp  point  at  which  the  flocculation  be- 
gins suddenly — like,  for  instance,  the  beginning  of  boiling  at  a  def- 
inite temperature — but  is  rather  a  range  of  concentrations  inside 
which  the  flocculating  effect  begins  and  rises  more  or  less  gradually 
to  its  maximum. 

The  different  acids  and  salts  vary  greatly  in  flocculating  power, 
but  these  variations  have  not  been  investigated  with  precision. 
Among  typical  colloids  such  as  colloidal  metals  there  are  many  cases 
in  which  the  flocculating  action  of  added  salts  appears  to  increase 
rapidly  with  rise  in  the  valence  of  the  flocculating  ion.  The  salts  of 
univalent  elements  are  least  active,  those  of  bivalent  elements  some- 
what more  active,  those  of  the  trivalent  elements  still  more  active, 
and  so  on.  However,  there  are  many  exceptions,  and  general  ap- 
plication of  the  rule  is  not  possible.  Doubtless  further  investiga- 
tion will  supply  principles  for  the  prediction  of  the  flocculating 
powers  of  various  salts,  but  at  present  these  powers  must  be  re- 
garded as  individual  and  specific. 

In  solutions  of  the  alkalies  the  relations  are  more  complex.  Fig. 
2  gives  the  effect  of  potassium  hydroxide  on  the  degree  of  floecula- 
tion  of  kaolin  suspensions  as  determined  by  F.  K.  Cameron  and  me.11 
It  is  apparent  that  the  degree  of  flocculation  in  pure  water  is  not 
zero,  but  is  importantly  greater  than  in  some  of  the  alkaline  solu- 
tions. 

There  is  again  the  phenomenon  of  the  threshhold  concentration, 
but  when  the  threshhold  is  passed,  the  effect  is  a  decrease  rather 
than  an  increase  in  the  degree  of  flocculation  and  there  is  a  zone  of 

I'Cameron  and  Free,  Science  (n.s.),  Vol.  32,  p.  482  (1910);  Free,  Jour. 
Frank.  Inst.,  Vol.  169,  pp.  430-4  (1910). 


318 


FLOTATION 


deflocculation  reaching  to  a  concentration  of  nearly  1  gramme  per 
litre.  As  concentration  increases  beyond  this,  there  is  an  increased 
flocculation,  surpassing  at  about  4  gm.  per  litre  the  degree  of  floc- 
culation  attained  in  pure  water  and  rising  thenceforth  to  a  max- 
imum of  flocculation  at  about  30  gm.  per  litre.  In  greater  concentra- 
tions there  is  a  decrease,  which,  however,  may  be  in  part  merely  ap- 
parent and  due  to  increasing  viscosity  and  density  of  the  solutions. 
The  characteristic  deflocculatirfg  effect  of  alkali  appears  to  be  an 


1 

jo 

0 

/ 

K 

^^ 

X 

0) 

/ 

6 

/ 

<j> 

/ 

4. 

/ 

—  ' 

00.010.1  1.00      5   10               50        100                   300          500       700 

FIG.    2 

effect  over  a  certain   concentration  range  only.     At  higher  concen 
trations  there  is  a  flocculating  effect  not  unlike  that  of  the  acids  and 
neutral  salts. 

Concerning  the  effect  of  the  remaining  class  of  deflocculators,  the 
organic  colloids,  there  is,  paradoxically,  rather  less  of  precise  ex- 
perimentation but  more  of  theoretical  understanding.  Substances 
cf  this  class  tend  to  prevent  the  flocculation  that  normally  exists  or 
that  would  otherwise  occur  on  the  addition  of  flocculating  agents. 
It  is  matter  of  common  knowledge  that  glue,  gelatin,  and  the  like 
will  prevent  the  subsidence  of  suspensions,  and  the  similar  effects 
on  plastic  clays  have  long  found  commercial  employment.  It  is  sig- 
nificant that  these  deflocculating  effects  are  exhibited  only  by  col- 
loids composed  of  liquid  particles.  It  has  been  suggested  that  the 
protective  action  is  due  to  the  coalescence  of  the  liquid  droplets  of 
the  colloid  with  the  particles  of  the  suspension  that  it  is  stabilizing. 
In  this  manner  liquid  films  of  the  protective  colloid  are  formed 
ftbout  the  particles  of  the  suspension,s  and  the  resultant  change  in 


COLLOIDS  319 

surficial  properties  is  supposed  to  be  responsible  for  the  failure  of 
these  particles  to  flocculate  and  subside.  There  is  much  evidence 
favorable  to  this  conception  of  the  mechanism  and  it  is  generally  ac- 
cepted. 

It  is  important  to  note  that  most  mineral  powders,  including  all 
ordinary  slimes,  exhibit  a  considerable  degree  of  flocculation  when 
they  are  suspended  in  water  even  when  no  flocculating  agent  has 
been  added.  It  does  not  matter  whether  this  normal  flocculation  be 
regarded  as  a  property  of  the  pure  mineral  in  pure  water  or  con- 
sidered an  effect  of  the  traces  of  flocculating  substances  (for  in- 
p 'ance,  carbon  di-oxide)  present  in  ordinary  waters.  The  significant 
fact  is  that  normal  slime  is  always  more  or  less  flocculated.  Exces- 
sive colloidality  is  usually  due  to  the  presence  of  some  substance  or 
circumstance  that  acts  as  a  deflocculator  and  destroys  or  prevents 
such  flocculation  as  would  otherwise  occur.  It  becomes  important, 
therefore,  to  search  out  the  cause  or  causes  responsible  for  this  de- 
flocculation.  It  is  natural  to  think  of  alkalies  or  of  organic  colloids, 
both  of  which  are  known  to  be  deflocculators.  Traces  of  alkali  in  ores 
are  not  impossible,  especially  in  highly  weathered  ores,  which  are  most 
subject  to  colloidal  difficulties.  That  the  alkali  can  reach  ordinarily  a 
concentration  sufficient  to  develop  the  deflocculating  effect  is  less  prob- 
able. The  glue-like  colloids  are  not  to  be  expected  in  slimes  except  in 
those  rare  cases  in  which  slime  or  mill-water  has  become  contaminated 
with  decaying  vegetation  or  other  organic  material.  If  excessive  col- 
loidality in  general  is  due  in  any  degree  to  the  deflocculating  action  of 
emulsoid  colloids  it  must  be  because  of  the  presence  of  some  inorganic 
emulsoid  and  the  only  such  emulsoid  now  known  and  at  all  probable  in 
rock-powders  is  colloidal  silicic  acid.  This  substance  has  never  been 
identified  in  slime  but  it  is  possible  that  it  is  produced  superficially 
on  particles  of  silicate  minerals  by  the  action  of  water  or  water  con- 
taining dissolved  carbon  di-oxide.  Cushman12  has  observed  surface 
alterations  of  silicate  fragments  after  long  grinding  with  water, 
and  these  alterations  may  correspond  to  something  of  this  kind.  It 
is  difficult  to  see  how  any  such  alterations  could  occur  on  sulphide 
particles  or  any  minerals  other  than  silicates,  but  the  entire  matter 
of  deflocculation  in  slime  is  so  little  known  that  speculation  is  of 
small  value.  Detailed  experimentation  is  essential  to  a  better  un- 
derstanding of  the  matter  and  this  experimentation  may  disclose 
active  causes  now  entirely  unsuspected. 


i2U.  S.  Department  of  Agriculture,  Bureau  of  Chemistry,  Bull.  92,  24  pp 
(1905). 


320  FLOTATION 

Aside  from  the  matter  of  removing  the  cause  of  excessive  defloc- 
culatiori,  if  that  cause  can  be  discovered,  there  is  a  possiblity  of  in- 
creasing the  degree  of  flocculation  by  the  addition  of  flocculating 
salts  or  acids,  as  suggested  especially  by  Ashley.13  From  the  curve 
of  Fig.  1  it  is  apparent  that  the  minimum  active  concentration  (the 
threshhold  concentration)  of  sodium  chloride  is  not  high,  and  this 
is  true  of  most  of  the  flocculating  salts.  There  is  nothing  inherently 
impracticable  in  the  use  of  such  flocculating  agents  in  ore-dressing; 
this  is  already  done  in  several  industries  and  is  a  common  procedure 
in  slime-testing,  and  in  the  analytical  laboratory  generally.  An  im- 
portant series  of  experiments  on  the  action  of  flocculating  agents  on 
slimes  has  recently  been  reported  by  Kalston.14  Other  experiments 
(with  common  salt  and  with  ferrous  sulphate)  have  been  reported 
by  Laist  and  Wiggin,15  whereas  Caldecott16  has  observed  in  practice 
the  reverse,  or  deflocculating,  effect  of  caustic  soda.  In  this  connec- 
tion it  should  be  noted  that  the  acid  or  other  solutions  used  in  the 
several  leaching  processes,  and  probably  also  the  usual  cyanide  so- 
lutions, have  a  flocculating  action  that  is  not  unimportant,  although 
the  employment  of  these  solutions  is  for  other  ends. 

A  word  must  be  devoted  to  the  use  of  lime  as  a  flocculating 
agent,  this  material  having  been  used  by  a  number  of  engineers.17 
At  first  sight  it  would  appear  improbable  that  lime  could  have  a 
purely  physical  flocculating  action,  lime  being  an  alkali  and  the 
characteristic  effect  of  small  concentrations  of  alkali  appearing  to  be 
a  deflocculation  rather  than  the  reverse.  There  is  nevertheless  a 
certain  flocculating  action  exhibited  by  lime,  even  under  laboratory 
conditions,  and  it  appears  that  the  hydroxides  of  calcium,  and  probably 
of  magnesium,  do  not  behave  exactly  like  potassium  and  sodium  hy- 
droxides. It  appears  probable,  also,  that  certain  purely  chemical 
factors  enter  as  well  and  that  the  efficacy  of  lime  as  a  clarifier  is  due  in 
part  to  chemical  reactions  of  the  same  sort  as  those  that  control,  for 
instance,  the  action  of  aluminum  salts  in  clarifying  water.  These 
clarifying  actions  apparently  depend  upon  the  formation  by  chem- 
ical reaction  of  some  flocculent  precipitate  that  entangles  and  sweeps 
down  the  suspended  particles.  Probably  the  occasional  cases  of 
clarification  by  organic  colloids18  belong  to  the  same  class. 


.  A.  I.  M.  E.,  Vol.  41,  pp.  380-95  (1910). 

rf  Min.  Jour.,  Vol.  101,  pp.  763-769,  890-894,  990-994   (1916). 
i»Bull.  A.  I.  M.  E.,  No.  92,  pp.  2201-16  (1914). 
ieProc.  Ch.em.  Met.  Soc.,  S.  A.,  Vol.  2,  pp.  381-29   (1898). 
i^See,  for  instance,  Richards,  'Ore  Dressing,'  Vol.  2,  p.  1149,  and  Vol    3. 
pp.  1416-17    (1903  and  1909). 

i«See  Ralston,  loc.  cit.  N 


COLLOIDS  321 

The  preceding  discussion  of  the  causes  of  excessive  colloidality 
of  slime  may  be  summarized  as  follows.  The  necessary  conditions 
for  the  production  of  a  colloidal  slime  are  two:  (1)  great  fineness 
of  particle  of  at  least  a  part  of  the  slime;  (2)  a  low  degree  of  floc- 
eulation  of  this  finely-divided  material.  Both  conditions  are  neces- 
sary. Neither  is  sufficient  alone.  It  is  useless  to  enter  here  into  the 
question  of  fineness  of  particle  or  its  possible  control.  Usually  such  a 
degree  of  control  as  might  entirely  prevent  the  production  of  a  very 
fine  material  is  not  practicable,  and  no  less  degree  of  control  will  be 
of  much  assistance  against  colloidal  troubles.  The  degree  of  floccu- 
lation  will  be  increased  by  dissolved  salts  and  acids  in  practically 
all  concentrations  and  by  alkalies  in  certain  concentrations,  mostly 
high.  It  will  be  decreased  by  low  concentrations  of  some  alkalies  and 
by  the  presence  of  organic  gelatinous  coatings,  in  the  rare  cases  when 
these  are  present.  It  is  possible  that  surface  alteration  of  silicate  par- 
ticles, or  some  other  cause,  may  produce  colloidal  silicic  acid,  which 
may  then  act  as  an  emulsoid  deflocculator.  If 'this  is  due  to  surface 
alteration  of  the  particles  it  will  probably  be  favored  by  long-continued 
grinding  or  by  storage  in  contact  with  water,  especially  in  the  presence 
of  carbon  di-oxide,  as,  for  instance,  under  long  exposure  to  the  atmos- 
phere. High  temperatures  also  favor  this  alteration.  There  are  prob- 
ably many  other  factors  affecting  the  degree  of  flocculation  but  they  re- 
main unknown. 

Ignoring  minor  uncertainties  and  assuming  a  slime  of  constant 
fineness,  rules  for  practical  procedure  may  be  stated  thus:  colloidal- 
ity will  be  increased  by  (1)  the  presence  of  small  amounts  of  free 
alkali  (except  lime),  (2)  prolonged  grinding  or  long  exposure  to  water 
or  the  atmosphere,  (3)  grinding  or  storage  at  high  temperatures,  (4) 
the  presence  of  organic  materials  such  as  would  be  supplied  by  decay- 
ing animal  or  vegetal  matter.  Colloidality  will  be  decreased  by  the 
avoidance  of  the  four  conditions  just  cited  and  also  by  (1)  the  presence 
in  solution  of  acids  or  of  neutral  salts  or  of  certain  alkalies  in  certain 
concentrations  and  (2)  rapid  grinding  and  handling.  The  relative 
quantitative  importance  of  the  various  factors  mentioned  and  the  de- 
cision as  to  which  should  be  selected  as  a  means  of  practical  improve- 
ment will  depend  upon  local  conditions  different  in  each  case.  In  gen- 
eral, the  presence  of  organic  matter  has  the  most  effect,  but  is  rarely 
encountered.  Next  in  quantitative  importance  is  the  presence  of  dis- 
solved acids,  salts,  or  alkalies.  Of  much  less  effect  is  the  time  of  grind- 
ing, or  storage  unless  it  runs  into  years,  and  of  still  less  effect  are 


322  FLOTATION 

changes,  between  usual  limits,  in  the  temperature  of  grinding  or  stor- 
age. 

With  the  recent  remarkable  development  of  flotation  processes  much 
interest  has  been  focused  on  the  fact  that  these  processes  work  much 
less  successfully  on  'very  fine'  slime  than  on  material  of  larger  par- 
ticles. The  failure  is  frequently  ascribed  to  colloidal  difficulties  in 
slimes.  It  is  difficult  to  discuss  this  matter  usefully.  The  basic 
theory  of  the  flotation  process  is  not  known  and  no  theory  has 
proved  generally  satisfactory.  Accordingly  the  following  sugges- 
tions are  offered  tentatively  and  merely  as  a  contribution  to  the  cur- 
rent discussion.  Only  from  the  slow  progress  of  experimentation 
can  one  expect  a  dependable  theory  of  the  flotation  processes  or  of 
the  relations  of  colloidal  theory  to  them. 

Regardless  of  ultimate  theory  it  seems  evident  that  the  essen- 
tial thing  in  the  flotation  process  is  the  tendency  of  certain  min- 
erals to  attach  themselves  to  films  or  globules  of  oil  or  to  complexes 
consisting  of  oil-globules  and  air  (or  gas) -bubbles.  This  tendency 
of  attachment  or  adhesion  varies  with  different  minerals  (as  well  as 
with  different  oils)  and  thus  provides  a  possibility  of  mineralogical 
separations.  The  various  matters  of  froth  production,  gravitational 
separation,  generation  or  incorporation  of  the  air  or  gas,  and  the 
like,  are  all  secondary,  from  my  viewpoint,  to  the  fundamental  mat- 
ter of  the  differential  attachment  of  minerals  to  the  oil  or  the  oil- 
gas  complex.  And  so  far  as  the  size  or  mineral  nature  of  the  parti- 
cles are  concerned  interest  may  be  confined  to  the  attachment  be- 
tween the  mineral  and  the  oil.  The  attachment  of  gas-bubble  and 
oil-film  or  the  maintenance  of  whatever  kind  of  oil-gas  complex  is 
desired  may  be  important  to  the  success  of  the  process  but  it  will 
depend  upon  the  mutual  properties  of  oil  and  gas  and  not  upon  the 
properties  of  the  mineral  particles.  These  matters  can  have  no  di- 
rect effect  on  the  attachment  between  the  mineral  and  the  oil.  It 
seems  probable,  therefore,  that  answers  to  questions  concerning  the  in- 
applicability of  flotation  to  slimes  are  to  be  sought  in  the  peculiar- 
ities of  the  forces  controling  the  oil-mineral  attachment. 

It  is  customary  to  refer  to  these  forces  as  interfacial  tensions.  This 
is  merely  a  matter  of  words.  The  fact  seems  to  be  that  surfaces  of 
contact  between  dissimilar  substances  have  peculiar  properties,  which 
properties  are  instanced  by  adsorption  and  the  surface-tension  of 
liquids  and  which  have  been  referred  to  above  as  important  among  the 
characteristics  of  colloids.  It  appears  that  the  surficial  layer  of  atoms 
in  any  mass  of  matter  has  properties  somewhat  different  from  those  of 


COLLOIDS  323 

atoms  within  the  mass.  When  two  masses  of  different  kinds 
of  atoms  are  in  contact  the  one  kind  of  atoms  may  affect  the  other 
kind  across  the  surface,  and  hence  the  differences  in  behavior  of  sur- 
ficial  atoms,  which  differences  constitute  the  'properties  of  the  surface,' 
may  depend  upon  the  natures  of  both  the  substances  in  contact. 
The  fundamental  theory  of  these  differences  in  the  surficial  lay- 
ers of  atoms  is  unknown  but  the  recent  papers  of  Langmuir19  are  most 
suggestive. 

The  special  characteristics  of  surfaces  are  exhibited,  in  the  main, 
by  two  things:  adsorption  and  the  surface-tension  of  liquids.  Adsorp- 
tion has  been  referred  to  above  as  the  tendency  of  dissolved  substances 
to  concentrate  at  the  surface  of  the  liquid,  either  a  free  surface  exposed 
to  the  atmosphere  or  a  surface  in  contact  with  solids.  The  best  in- 
stances are  furnished  by  finely  divided  solids,  which  have  the  great 
ratio  of  internal  surface  to  mass  mentioned  above.  Thus,  powdered 
charcoal  will  remove  nearly  all  of  certain  dyes  from  their  aqueous  so- 
lutions by  adsorption  alone,  without  chemical  reaction  or  destruction 
of  the  dye.  Surface-tension  is  shown  in  the  tendency  of  liquid  glob- 
ules to  take  spherical  form  and,  in  general,  the  tendency  of  all  liquid 
surfaces  to  contract  whenever  not  prevented  by  external  force.  The 
liquid  may  be  supposed  to  draw  itself  together  into  the  most  compact 
shape  possible.  Among  other  peculiarities,  both  adsorption  and  sur- 
face-tension have  the  characteristic  of  varying  with  the  curvature  of 
the  surface,  especially  when  the  radius  of  curvature  is  very  small.  Thus 
substances  in  very  fine  fragments  or  droplets  have  properties  signifi- 
cantly different  from  the  properties  of  the  same  substances  in  mass. 
For  instance,  the  solubilities  and  vapor-pressures  are  greater.  Here 
again  the  mechanism  is  imperfectly  understood,  but  it  is  not  neces- 
sary to  the  present  argument. 

Returning  to  the  conditions  present  in  the  flotation  process,  if  the 
essential  matter  is  the  establishment  and  persistence  of  the  attach- 
ment between  mineral  and  oil  and  if  the  tendency  to  this  attachment 
varies,  as  do  adsorption  and  surface-tension,  with  the  curvature  of  the 
active  surface,  it  is  evident  that  the  tendency  to  attachment  may  vary 
markedly  with  the  size  of  the  mineral  particle.  As  a  particle  de- 
creases in  size  the  average  radius  of  curvature  becomes  very  short.  At- 
tachment to  the  oil  might  be  rendered  more  easy  or  less  easy — one 
could  not  decide  which,  a  priori — but  it  would  be  likely  to  be  affected 
in  some  way.  A  further  complication  is  introduced  by  the  matter  of 


^Metall.  d  Chem.  Eng.,  Vol.  15,  pp.  468-470   (1916);    Jour.  Amer.  Chem. 
Soc.,  Vol.  38,  pp.  2221-2295  (1916). 


324  FLOTATION 

adsorbed  films  on  the  mineral  particles.  These  particles  do  not  pre- 
sent to  the  oil-globules  mineral  faces  fresh  from  cleavage  and  there- 
fore clean.  The  surface  actually  presented  has  been  in  contact  with 
water  or  air  or  both,  and  the  water  has  probably  contained  many  dis- 
solved substances.  It  follows  that  the  oil  must  not  only  attach  itself 
to  the  mineral  surface  but,  in  order  to  do  so,  must  displace  from  that 
surface  a  film  of  water,  air,  or  some  dissolved  material  or  materials 
adsorbed  from  the  water  with  which  the  particle  was  previously  in  con- 
tact. It  is  probable,  though  I  do  not  think  it  is  certain,  that  such  at- 
tached films  of  water,  air,  or  other  adsorbed  substances  are  held  more 
tenaciously  when  the  particles  are  small  than  when  they  are  large.  If 
so,  it  is  possible  that  such  adsorbed  films  might  prevent  the  necessary 
oil-attachment  in  slime  but  not  in  larger  particles, 

It  is  not  necessary,  of  course,  that  the  disturbing  effects  of  small 
particle-size  should  operate  always  or  merely  to  prevent  oil-attach- 
ment. The  flotational  separation  would  be  equally  impaired  if 
the  tendency  to  oil-attachment  were  increased,  provided  that  this  in- 
crease affected  the  non-metallic  minerals  as  well  as  the  metallic.  All 
that  is  necessary  to  destroy  the  efficacy  of  the  notation  process  is  that 
something  should  impair  the  differential  character  of  the  attachment 
of  oil  to  different  minerals.  The  argument  outlined  above  will  indicate 
that  this  is  quite  to  be  expected  when  the  mineral  particles  become 
unduly  small.  As  particle-size  decreases  the  properties  of  the  surface 
become  more  important,  those  of  the  mass  (for  instance,  specific  grav- 
ity) become  less  so.  Small  particles  tend  to  behave  more  and  more  alike 
the  smaller  they  are,  regardless  of  the  minerals  (or  other  substances) 
of  which  they  happen  to  be  composed.  Much  significant  and 
suggestive  work  indicates,  in  general,  that  surfaces  of  different  sub- 
stances are  much  more  nearly  alike  in  essential  physical  properties 
than  are  masses  of  the  same  substances. 

It  is  not  'particularly  encouraging  to  come  out  of  the  argument 
merely  with  the  conclusion  that  the  inefficacy  of  the  flotation  process 
with  slimes  is  to  be  expected.  One  hoped  for  suggestion  as  to  how  the 
disability  might  be  removed.  It  does  not  seem  probable  that  such  sug- 
gestions will  be  forthcoming  until  the  nature  of  the  surface  properties 
of  substances  shall  have  been  elucidated  by  further  investigation.  Im- 
provements made  in  the  meantime  in  the  application  of  the  flotation 
process  to  slimes  are  likely  to  be  purely  empirical  and  largely  acci- 
dental. Such  improvements  have  been  made  and  undoubtedly  will  be 
repeated  but  it  is  to  be  hoped  that  detailed  investigation  of  the  prop- 
erties of  surfaces  will  furnish  before  long  a  surer  ground  of  progress. 


COLLOIDS  325 

SELECTED  WORKS  ON  COLLOIDS 

ASHLEY,  H.  E.,  'The  Chemical  Control  of  Slimes.'  Trans.  A.  I.  M.  E., 
Vol.  41,  pp.  380-395  (1910). 

BURTON,  E.  F.,  'The  Physical  Properties  of  Colloidal  Solutions.'  Lon- 
don and  New  York,  1916,  194  pp. 

CASSUTO,  L.,  'Der  Kolloide  Zustand  der  Materie.'  Leipzig,  1913, 
252  pp. 

FREUNDLICH,  HERBERT,  'Kapillarchemie.'    Leipzig,  1909,  565  pp. 

HATSCHEK,  EMIL,  'An  Introduction  to  the  Physics  and  Chemistry  of 
Colloids.'  2nd  ed.,  London  and  Philadelphia,  1916,  102  pp. 

OSTWALD,  WOLFGANG,  'Grundriss  der  Kolloidchemie. '  Dresden.  1909, 
509  pp.  The  first  half  of  a  second  revised  edition  has  been  issued 
(1911,  329  pp.)  and  re-printed  without  change  (1913)  as  the 
first  half  of  a  third  edition.  The  second  half  has  not  been  issued 
either  in  the  second  or  third  editions.  The  second-third  German 
edition  has  been  translated  into  English  by  Martin  H.  Fischer 
under  the  title  'A  Handbook  of  Colloid-Chemistry,'  Philadelphia, 
1915,  266  pp. 

TAYLOR,  W.  W.,  'The  Chemistry  of  Colloids, r London,  1915,  328  pp. 

ZSIGMONDY,  RICHARD,  'Ziir  Erkenntniss  der  Kolloide,'  Jena,  1905,  185 
pp.  Translated  and  revised  edition  in  English  by  J.  Alexander. 
New  York,  1909,  245  pp. 

ZSIGMONDY,  RICHARD,  'Kolloidchemie.'  Leipzig,  1912,  281  pp. 


326  FLOTATION 


FLOTATION  TRIBULATIONS 

By  JACKSON  A.  PEARCE 
(From  the  Mining  and  Scientific  Press  of  September  16,  1916) 

Idaho  Springs  lies  within  a  heavily  mineralized  district  covering 
the  better  part  of  two  counties,  Clear  Creek  and  Gilpin,  in  Colorado. 
Gold,  silver,  lead,  copper,  zinc,  molybdenum,  tungsten,  and  uranium 
in  most  of  their  manifold  mineralogical  forms,  occur  in  commercial 
quantities.  In  the  ores  they  occur  individually  and  collectively, 
offering  an  excellent  field  for  metallurgical  research.  Within  easy 
reach  of  Denver  with  its  milling  machinery  and  of  Golden,  the  seat  of 
the  Colorado  School  of  Mines,  this  district  is  utilized  as  a  testing 
yard  for  processes  and  machinery,  falling  intermediate  between  the 
laboratory  and  the  modern  plant.  Thus  it  has  become  a  museum  of 
the  world's  metallurgical  processes.  One  can  find  here  almost  any- 
thing from  a  long-torn  to  an  electrolytic  refinery. 

Flotation,  the  most  recent  process  to  be  placed  on  exhibition,  had 
been  in  operation  in  a  couple  of  local  plants  a  few  months  before  any 
decision  had  been  made  to  install  a  machine  at  the  Argo  mill.  Much 
laboratory  work  had  been  done  on  flotation,  but  as  concentration  and 
cyanidation  had  been  running  smoothly  the  desire  to  change  was  not 
burning.  However,  tests  showed  that  it  might  be  useful  on  certain 
low-grade  silver  ores  not  particularly  well  adapted  to  cyanidation. 
With  this  end  in  view  a  machine  was  installed. 

Having  dedicated  the  better  part  of  my  life  to  cyanidation,  and 
having  contributed  largely  to  the  adaptation  of  cyanidation  to  these 
ores,  I  entered  upon  flotation  with  many  misgivings,  and  these  few 
notes  may  be  taken  as  a  confession  of  a  cyanider — not  that  of  a  flota- 
tion expert. 

The  preliminary  tests  were  made  in  a  home-made  single-cell  ma- 
chine. Especial  attention  was  given  to  an  ore  assajdng  0.12  to  0.40  oz. 
gold,  8  to  20  oz.  silver,  and  a  strong  trace  each  of  copper,  lead,  and  zinc. 
On  account  of  its  relatively  high  silver-value  this  ore  is  not  particu- 
larly amenable  to  cyanidation.  Although  the  gold  in  these  ores  yields 
readily  to  cyanidation  the  silver  is  backward,  60%  being  the  average 
extraction.  These  tests  were  carried  out  with  a  view  to  establishing 
the  best  conditions  as  to  speed  of  impellers,  consistence  of  pulp,  com- 
bination of  oils,  temperature,  and  fineness  of  ore.  No  critical  condition 


FLOTATION    TRIBULATIONS  327 

was  established  in  any  of  these  lines,  a  satisfactory  extraction,  85  to 
90%,  resulting  from  within  wide  limits  of  each.  Other  gold  ores 
yielded  a  good  extraction  by  flotation,  but  not  sufficiently  to  enthuse 
one  as  to  its  preference  over  cyanidation. 

A  flotation  machine  of  100  tons  capacity  was  installed  to  handle 
silver  ores  only,  giving  us  two  distinct  flow-sheets  within  the  mill.  The 
flotation  system  comprised  stamping  to  16-mesh,  classifying  in  Dorr 
machines,  cencentrating  on  Card  tables,  re-grinding  in  a  tube-mill,  re- 
concentrating  on  slime-tables,  and  thickening  the  combined  slime  and 
re-ground  sand  for  flotation.  With  this  arrangement  we  expected  to 
get  55  to  65%  extraction  on  the  tables,  and  50  to  60%  on  the  flotation 
machine,  or  a  mill  extraction  of  75  to  85%,  which,  considering  the 
laboratory  extraction  of  85  to  90%,  was  a  conservative  estimate. 

In  the  first  three  weeks  of  operation  the  extraction  on  the  primary 
tables  was  50%,  but,  contrary  to  expectation,  the  extraction  in  the 
flotation  machine  was  nothing.  Before  table  concentration  this  ore 
carried  a  trace  each  of  galena,  chalcopyrite,  and  blende,  with  sufficient 
pyrite  to  give  a  concentration  ratio  of  4:1.  The  exceedingly  small 
amount  of  flotation-concentrate  was  composed  of  galena,  chalcopy- 
rite, and  blende,  with  an  abundance  of  silica  but  very  litle  pyrite.  The 
amount  of  this  product  was  not  sufficient  to  make  an  appreciable  dif- 
ference in  the  assays  of  feed  and  discharge.  I  may  add  that  the  assays 
covering  this  test  averaged  a  shade  higher  for  the  discharge  than  for 
the  feed.  This  was  disconcerting,  to  put  it  mildly.  Three  weeks  is  not 
a  long  time  in  which  to  perfect  a  process,  but  it's  a  mighty  long  time 
to  watch  half  the  value  of  the  ore  going  into  the  creek. 

During  this  time  we  gave  particular  attention  to  oils.  According 
to  information  gathered  from  reports,  and  from  personal  conversation 
with  flotation  metallurgists  and  salesmen,  it  seemed  that  the  oil  was 
the  most  important  consideration  in  flotation.  It  is  generally  believed 
that  different  ores  require  different  oils.  Adjoining  properties  on  the 
same  ore  deposit  seem  unable  to  use  the  same  combination  of  oils.  In 
this  respect  the  outlook  for  flotation  here  was  painful  to  consider, 
since  this  is  a  custom-mill  fed  by  a  multitude  of  mines  in  a  district 
producing  a  great  variety  of  ores.  During  the  three  weeks  we  made 
exhaustive  tests,  covering  a  wide  range  of  oils,  trying  one  after  another, 
individually  and  in  combinations.  Operators  seem  to  have  favorite 
places  in  the  system  for  feeding  oils,  some  favoring  the  batteries,  others 
the  tube-mill,  and  so  on,  down  to  the  last  cell  in  the  machine.  We 
covered  everything  from  the  coarse  crusher  to  the  tail-race.  Special 
mixers  or  emulsifiers  are  in  common  use,  and  we  installed  one.  II 


328 


FLOTATION 


seemed  to  make  little  difference  what  oil,  how  much,  or  where  fed ;  the 
froth  was  always  the  same — abundant  and  barren.  At  times  it  was 
excellent  to  the  view,  according  to  one  metallurgist,  *  *  a  most  beautiful 
froth/'  three  to  six  inches  deep,  bluish  black,  and  covering  the  entire 
froth-cell.  At  other  times  it  was  over-abundant,  rolling  over  both 
ends,  back  and  front  of  the  machine,  developing  so  rapidly  that  it 


pulley 


FIG.   1 

required  the  best  efforts  of  two  men  to  sluice  it  to  the  creek.  We  ran 
it  in  this  manner  for  24  hours — not  that  we  wanted  the  froth,  but  to 
ascertain  the  ratio  of  extraction  to  quantity  of  froth.  Although  the 
total  amount  of  material  floated  was  appreciable,  there  was  no  differ- 
ence in  assays  of  heading  and  tailing,  clearly  indicating  non-selective 
action. 

We  used  oils  furnished  by  several  companies,  including  crude 
wood-oils,  pine-tar  oils,  tar,  wood-creosote,  crude  and  refined  turpen- 
tine, asphalt,  coal-tar,  gasoline,  coal-oil,  gas-oil,  and  coal-tar  creosote. 

Regular  examination  of  the  tailing  showed  pyrite  in  great  plenty, 
every  particle  of  which  was  thoroughly  oiled,  and  easily  floated  from 
the  gangue  by  simple  panning.  Was  there  some  condition  in  the  ma- 
chine to  disengage  these  oiled  particles  from  the  froth  ?  Or,  were  they 
ever  attached  to  the  froth?  Or  to  the  bubbles  preceding  the  froth? 
The  machine  was  built  with  an  intricate  set  of  baffles  following  the 
agitation,  through  the  tortuous  course  of  which  the  bubbles  might 
have  dropped  their  burden.  We  simplified  the  baffles,  trying  a  dozen 


FLOTATION    TRIBULATIONS  329 

different  kinds,  one  after  another,  terminating  a  heart-breaking  task 
with  no  baffles  at  all.  The  machine  worked  as  well  without  as  with 
baffles;  so  why  baffles? 

The  mineral  particles  were  well  oiled,  but  lacked  the  balloon  ar- 
rangement necessary  to  conduct  them  to  the  surface.  Perhaps  the 
agitators  were  not  fast  enough  to  churn  the  air  into  the  oil.  Most  peo- 
ple emphasize  the  importance  of  peripheral  speed,  some  giving  1500 
ft.  per  minute  as  the  best,  extraction  and  power  considered.  We  were 
operating  at  this  speed,  but  increased  it  by  stages  to  2100  ft.  The 
motor  would  not  carry  this  load  for  more  than  a  few  hours  at  a  time ; 
besides,  the  results  were  no  better  than  at  1500.  We  decreased  the 
speed  to  1200,  and,  finding  it  more  economical  in  power  and  just  as 
efficient  in  extraction,  left  it  at  that.  Later  on  it  was  reduced  to  1100. 
Turning  our  attention  to  ore-fineness  we  found  a  wide  range  of  recom- 
mendations, some  operators  recommending  —  40,  some  —  60,  others 
- 100,  and  yet  others  close  to  -  200,  nearly  all  contending  that  the 
finer  the  ore  the  better  was  the  flotation.  My  own  laboratory  experi- 
ments on  this  particular  ore  gave  good  extractions  on  a  12-mesh  prod- 
uct. We  tried  everything  from  a  16-mesh  product  direct  from  the 
stamps  to  a  product  95%  of  which  would  pass  a  200-mesh  screen. 
While  there  were  no  encouraging  signs  within  this  range,  the  advan- 
tage, though  small,  lay  with  the  coarser  product. 

During  these  tests  (from  January  to  March  this  year)  the  tempera- 
ture hovered  around  zero,  at  times  reaching  12  to  15°  below.  Mill- 
water  was  close  to  the  freezing-point,  and  great  care  had  to  be  exercised 
to  prevent  pipes  and  launders  freezing.  Although  many  consider 
higher  temperatures,  say  70°  P.,  essential  to  good  work,  we  were  un- 
able to  attain  this  economically,  for  lack  of  facilities  for  returning  the 
mill-water.  Nevertheless,  to  satisfy  ourselves  on  this  point,  we  turned 
the  full  capacity  of  a  boiler  into  the  feed,  thereby  raising  the  tempera- 
ture to  60°  P.  After  six  hours  at  this  temperature  the  difference  in 
effect  was  in  no  way  sufficiently  marked  to  justify  heating. 

Next  we  turned  our  attention  to  consistence,  the  general  report 
favoring  6  : 1  for  very  fine  pulp  down  to  3 : 1  for  sand.  We  covered  a 
range  from  20 : 1  to  2^ :  1,  coming  to  the  conclusion  that  we  were  nosing 
the  wrong  scent. 

It  might  be  assumed  that  inexperience  in,  or  prejudice  against,  the 
process,  to  the  one  or  the  other  of  which  most  failures  are  due,  was 
at  the  bottom  of  our  troubles.  While  I  have  spent  most  of  my  life  at 
cyanidation,  and  greatly  value  the  process,  and  perhaps  have  a  soft 
spot  in  my  heart  for  it,  the  fear  of  failure  in  any  undertaking  greatly 


330  FLOTATION 

exceeds  any  prejudices  I  may  have  against  it.  Also,  it  may  be  said, 
we  had  the  personal  services  of  several  distinguishel  flotation  metal- 
lurgists, no  one  of  whom  was  able  to  suggest  any  change  leading  to 
decided  improvement. 

It  was  the  firm  conviction  of  one  engineer  that  the  machine  was 
over-loaded.  Although  it  was  carrying  J  its  rated  load,  I  reduced  the 
feed  to  1/40  its  rated  capacity,  not  that  we  could  expect  to  operate  on 
that  basis,  but  to  get  a  clue  if  possible  to  the  trouble.  There  was  no 
improvement. 

At  last  we  did  what  at  first  we  would  have  done  with  any  other 
process :  we  investigated  the  theories.  But  with  flotation,  where  every- 
body has  gratifying  success  and  nobody  has  a  gratifying  theory,  it 
seemed  unreasonable  that  we  alone  should  need  a  theory.  Theories  of 
flotation  are  now  running  the  gauntlet  of  thoughtful  criticism  so 
essential  to  the  survival  of  the  fittest.  "Fittest"  in  this  instance  is 
not  amiss,  for  almost  all  theories  are  limited  to  certain  facts,  and  that 
theory  survives  or  is  accepted  which  is  fittest,  that  is,  which  fits  the 
greatest  number  or  widest  range  of  facts.  The  ionic  theory  of  chem- 
ical reactions  superseded  the  affinity  theory  by  virtue  of  its  being  more 
inclusive.  No  sooner  is  a  flotation  theory  advanced  than  there  arises 
a  brilliant  array  of  facts  tending  to  disprove  it,  or,  in  other  words,  to 
limiting  its  fitness,  so  that  in  the  present  state  of  the  subject  it  ill  be- 
comes us  dogmatically  to  assert  that  any  one  is  the  correct  theory, 
exclusive  of  all  others. 

The  early  efforts  to  establish  a  theory  involving  adhesion,  which  is 
only  a  begging  of  the  question,  and  one  involving  the  angle  of  contact 
or  angular  hysteresis,  have  given  way  to  those  of  more  apparent  merit 
involving  occluded  gases,  electro-statics,  and  interfacial  tension. 
Whether  any  one  of  these,  or  any  combination  of  them,  survives  is 
problematical. 

Regarding  the  application  of  the  theory  of  angular  hysteresis,  we 
assumed  that  the  pyrite  was  not  making  the  desired  angle  of  contact, 
and,  knowing  of  no  way  to  cause  it  to  do  so,  we  dismissed  the  subject. 

THEORY  OF  OCCLUDED  GAS.  The  theory  of  occluded  gas  so  ably 
advanced  by  Durell  appealed  to  me  in  its  tangibility.  All  substances 
occlude  gases,  the  tenacity  of  retention  being  more  pronounced  in  some 
than  in  others,  but  in  all  cases  capable  of  expulsion  by  osmotic  pres- 
sure, increased  temperature,  or  vacuum.  Only  by  virtue  of  this  oc- 
cluded gas  can  a  bubble  of  gas  be  attached  to  the  substance.  The 
sulphides  of  metals,  iron,  lead,  zinc,  etc.,  constituting  the  economic 
portion  of  the  ore,  are  more  tenacious  in  the  retention  of  the  occluded 


FLOTATION    TRIBULATIONS  331 

gas  than  silica,  lime,  feldspar,  etc.,  constituting  the  waste  portion  of 
the  ore.  Therefore  by  regulating  the  osmotic  pressure,  temperature, 
or  vacuum  the  occluded  gases  of  the  gangue-material  can  be  expelled 
entirely,  at  the  same  time  leaving  sufficient  gas  in  the  sulphide  to  act 
as  a  nucleus  in  the  formation  of  adhesive  gas-bubbles,  thereby  giving 
us  '  selective '  flotation.  Silica  was  coming  over  with  the  froth  in  pref- 
erence to  sulphides.  The  evident  procedure  was  to  expel  the  gas  from 
the  silica,  taking  care  not  to  expel  it  from  the  sulphides. 

We  had  already  tried  heat  with  no  success;  we  were  not  prepared 
for  trying  vacuum;  so  we  tried  osmotic  pressure.  To  increase  the 
osmotic  pressure,  we  increased  the  number  of  ions  by  the  addition  of 
some  easily  dissociated  solute,  say,  sulphuric  acid.  Acid  has  the  ad- 
vantage over  salts  in  its  power  to  reduce  the  surface-tension,  or  the 
'surten,'*  permitting  the  formation  of  bubbles.  Starting  with  a  very 
small  amount  of  acid  we  increased  it  gradually  to  20  Ib.  per  ton.  The 
more  we  added  the  more  disheartened  we  became. 

INTERFACIAL  TENSION.  Roughly  stated,  water  and  oil  (if  insolu- 
ble) in  contact  maintain  their  individual  faces,  the  oil  facing  the 
water,  the  water  facing  the  oil.  This  is  the  interface  of  the  two.  Now, 
introducing  a  solid,  say,  a  small  particle  of  ore,  it  is  found  to  have  three 
tendencies:  it  tends  to  enter  the  water  only;  it  tends  to  enter  the  oil 
only;  it  tends  to  enter  both  oil  and  water.  If  the  tendency  to  enter 
both  water  and  oil  is  sufficiently  marked  for  each  liquid,  it  remains 
between  the  two,  or  on  the  interface,  a  phenomenon  on  which  is  based 
the  theory  of  interfacial  tension.  This  was  wonderfully  exemplified 
in  our  machine,  the  only  drawback  being  that  it  was  the  silica  that 
displayed  a  preference  for  the  interface. 

ELECTRO-STATIC  THEORY.  Gas  and  oil  films  are  negatively  charged 
irrespective  of  the  electrolyte  in  which  they  are  formed.  Silica,  and 
perhaps  silicious  gangue,  is  negatively  charged  in  the  presence  of  the 
hydrogen  ion,  reversing  its  polarity  in  the  presence  of  the  hydroxyl 
ion.  Sulphides  are  perhaps  positively  charged.  The  mutual  attrac- 
tion of  oppositely-charged  bodies  together  with  the  mutual  repulsion 
of  similarly-charged  bodies  operate  to  produce  selective  flotation. 

On  this  assumption  we  examined  the  electrolyte:  mill-water  plus 
the  soluble  constituents  of  the  ore.  It  carried  copper  and  some  iron 
and,  among  other  things,  a  weak  trace  of  acid.  It  would  seem  logical 
to  acidify  it  more  strongly  to  ensure  a  negatively-charged  silica.  But 
in  acidifying  to  increase  the  osmotic  pressure  we  observed  that  it  im- 
proved neither  the  osmotic  nor  electro-static  effect.  Evidently  the 


*M.  &  S.  P.,  July  29,  1916. 


332  FLOTATION 

pyrite  particles  were  not  electrified,  or  else  were  unsuitably  charged. 
We  induced  electrification,  or  tried  it.  By  the  hit  or  miss  method  we 
attempted  to  get  an  electrolyte  that  would  make  a  more  desirable 
distribution  of  the  electric  charges.  We  tried  a  long  list  of  salts,  acids, 
and  bases,  organic  and  inorganic.  Nothing  especially  noteworthy 
resulted  from  these  experiments. 

By  this  time  we  had  been  operating  or  experimenting  nearly  three 
months,  all  the  time  at  high  tension.  I  had  exhausted  myself  of  ideas, 
likewise  the  entire  mill-crew,  and  every  visitor  to  the  mill.  I  pressed 
everybody  for  suggestions,  talked  bubbles  all  day  and  dreamed  bub- 
bles all  night.  It  certainly  seemed  that  we  had  left  nothing  undone 
that  should  have  been  done.  I  must  admit  that  the  extraction  had  been 
improving  gradually.  The  froth  was  making  a  better  selection  of 
material,  but  was  still  high  in  silica,  voluminous  and  difficult  to 
handle.  Our  endeavor  was  to  produce  less  froth  with  more  mineral, 
intensive  as  well  as  selective  flotation.  Exhausted  of  ideas,  we  drifted 
along  a  few  days,  when  to  our  great  surprise  and  for  no  apparent 
reason  whatever,  the  froth  so  long  sought  appeared.  The  voluminous 
tough  and  silicious  froth  had  given  way  to  a  thin  heavily-laden  froth 
with  a  greenish-yellow  cast  of  the  pyrite.  Simultaneous  with  it  the 
extraction  went  up  and  the  silica  down. 

When  the  recovery  increased  to  92%,  which  exceeded  our  expec- 
tations, we  felt  more  kindly  toward  flotation,  even  to  the  extent  of 
trying  it  on  ores  that  were  being  cyanided.  For  seven  days  we  ran 
flotation  and  cyanidation  side  by  side  on  the  same  ore  with  a  recovery 
of  96.2%  for  cyanidation  and  96.5%  for  flotation.  This  was  a  surprise 
from  which  we  have  not  yet  fully  recovered. 

Suspending  cyanidation,  we  applied  flotation  to  all  the  different 
ores  we  could  muster  to  the  mill.  The  results  were  so  gratifying,  cost 
and  recovery  considered,  that  cyanidation  was  abandoned. 

For  the  four  months  ending  July  31,  the  recovery  by  months  has 
been  95.01,  95.06,  95.5,  and  95.6%.  Recovery  by  metals:  gold, 
97.35%;  silver,  82.2%;  copper,  93.4%;  lead,  the  few  assays  would 
indicate  about  95% ;  zinc,  no  assays.  The  recovery  of  the  silver, 
though  considerably  higher  than  in  cyanidation,  is  still  unsatisfac- 
torily low.  This  is  contrary  to  the  impression  so  general  that  because 
a  mineral  floats  off  the  table  it  is  amenable  to  flotation.  Silver  floats 
off  the  table  to  a  greater  extent  than  copper,  yet  the  flotation  machine 
removes  a  greater  percentage  of  the  copper  than  of  the  silver.  Figures 
from  four  months  operation  show  a  recovery  on  table,  copper  64.3%, 
silver  63.9%;  on  the  flotation  machine,  copper  81.1%,  silver  50.7%. 


FLOTATION    TRIBULATIONS  333 

This  recovery  by  concentration  and  flotation  compares  agreeably  with 
the  best  cyanide  practice  under  the  most  favorable  conditions,  and 
when  viewed  in  the  light  of  the  wide  range  of  ores  treated  it  is  sur- 
prising. I  am  including  a  table  made  from  assays  of  lots  sampled 
giving  a  general  idea  of  the  range  covered. 

I  have  had  a  keen  desire  to  know  what  was  at  the  bottom  of  our 


Gold, 

Silver, 

Copper 

,  Lead, 

Gangrue 

Concentration 

1 

Oz. 
0.14 
0.18 

Oz. 
1.84 
11.60 

% 
trace 

% 
2.0 
trace 

quartz 
feldspar 

ratio  about 
10:1 
4:1 

Remarks 

2  . 

3  2.50 

7.50 

2.0 

1.5 

quartz 

3:1 

Gray  copper 

4. 

1.72 

6.88 

3.0 

feldspar 

2:1 

6. 

6. 

7. 
8 

0,74 
0.40 
0.62 
2.06 
1.96 
1.05 

0.58 
12.20 
4.40 
0.40 
1.30 
20.50 

1.4 

none 
1.0 
1.9 

none 
0.5 
8.0 

quartz 
feldspar 
talc 
quartz 
feldspar 
auartz 

40:1 
12:1 
10:1 
2:1 
5:1 
3:1 

Free  milling- 
20  years  on  dump 
40%  saved  on  tables 

Mostly  free  milling1 
Chalcopyrite 



9  
10.  . 

three  months'  troubles,  and  to  this  end  have  carried  on  the  operation 
under  different  conditions  as  to  oil,  temperature,  consistence,  etc.  In 
practice  we  are  using  crude  wood-creosote,  15%,  and  a  Wyoming  gas- 
oil,  85%,  this  being  one  of  the  best  two  combinations  found  in  the 
laboratory  tests.  We  ran  10  days  on  wood-tar  oil  and  gas-oil ;  ten  days 
on  crude  turpentine  mixed  wtih  coal-tar  creosote ;  2  days  on  pine-tar 
and  creosote  with  gas-oil ;  2  days  on  pine-oil  with  gas-oil ;  and  3  days 
on  wood-creosote  with  coal-oil,  in  all  cases  getting  the  same  high  ex- 
traction. During  our  early  efforts  to  find  the  right  combination  of  oils 
we  would  make  a  mixture  of  this,  that,  and  the  other  oil,  try  it  for  12, 
15,  or  24  hours  as  indications  suggested,  and  that  not  used  in  the  trial 
was  thrown  into  a  slop-barrel.  In  this  way  we  accumulated  a  barrel  or 
so  containing  every  conceivable  oil  on  which  we  could  lay  hold,  or- 
ganic and  mineral,  with  some  organic  acids,  such  as  oleic.  Running 
short  of  other  oils  one  day,  we  had  recourse  to  this  slop,  which  proved 
as  efficient,  entirely  so,  as  any  other  oil  used. 

As  to  temperature,  one  day  during  a  particularly  cold  snap,  we 
had  occasion  to  stop  the  machine  for  a  short  time,  during  which  ice  of 
considerable  thickness  formed  over  the  entire  machine.  When  we 
started  again  it  was  necessary  to  break  the  ice  to  remove  the  froth, 
yet  the  froth  was  never  more  heavily  laden  with  mineral  than  at 
that  time. 

To  test  the  influence  of  consistence,  we  allowed  the  entire  mill-flow, 
battery-water,  table-wash,  and  all  to  run  through  the  machine  for  three 
days.  The  consumption  of  oil  might  have  been  heavier,  but  the  re- 
covery was  not  impaired. 

Many   other  changes  were   made  involving  submergence,   speed, 


334  FLOTATION 

baffle,  though  regularly  we  use  no  baffles,  none  of  which  interfered 
with  the  extraction,  that  is,  noticeably  so.  The  problem  of  going 
backward  we  found  as  difficult  as  previously  it  was  to  go  forward, 
though  beset  with  much  less  worry. 

I  believe  that  oil,  temperature,  speed,  etc.,  each  has  its  own  influ- 
ence on  the  recovery,  but  within  wide  limits  this  can  be  measured  in 
fractions  of  1%.  I  believe  our  greatest  trouble  was  due  to  accumulated 
slime — colloidal  slime,  if  you  like.  Tests  not  yet  complete  seem  to 
show  that  not  the  absolute  amount  of  slime,  but  the  proportion  of 
slime,  is  the  disturbing  element. 

At  present  the  salient  features  of  the  process  are : 

Ore :  Pyritic,  containing  gold  and  silver,  with  small  amounts  each 
of  copper,  lead,  and  zinc,  concentrating  anywhere  from  50: 1  to  2:  1. 

Oil:  Wood  creosote  15%,  Wyoming  gas-oil  85%.  Much  trouble 
was  experienced  in  feeding  the  oil,  due  to  the  separation  of  tar,  closing 
the  openings  of  the  vessels.  To  obviate  this  I  devised  a  feeder  with  a 
rotating  cylinder  with  impressed  cups.  One  can  be  made  easily  by 
filling  the  central  part  of  a  plug-valve  with  metal  and  fixing  with 
shaft  as  shown  in  sketch.  This  has  been  working  quite  satisfactorily. 

Consistence :   4  or  6 : 1. 

Temperature :   That  of  the  mill. 

Screen  test:  minus  60.  The  grinding  is  more  for  the  purpose  of 
liberating  the  sulphides  from  the  gangue  than  for  preparing  the  lib- 
erated sulphides  for  flotation.  The  machine  will  handle  a  surpris- 
ingly coarse  product  if  it  follows  good  table-concentration. 

Speed:   1100  r.p.m. 

No  acids  or  other  reagents  are  used. 

The  froth  is  small  in  volume,  about  J  in.  thick,  covering  but  one- 
third  of  the  froth-cell.  It  is  removed  by  revolving  scrapers  made  of 
20-mesh  battery-screen.  The  screen-openings  are  small  enough  to 
prevent  the  froth  passing  back,  but  large  enough  to  pass  the  slime, 
thus  reducing  the  silica  in  the  concentrate. 


COST    DATA  335 


COST  DATA 

By  0.  C.  RALSTON 
(Written  especially  for  this  volume) 

THE  FIRST  COST  of  installing  flotation  machinery  is  low,  much 
lower,  in  fact,  than  the  other  machinery  that  is  necessary  to  prepare 
the  ore  for  flotation  and  to  treat  the  resulting  concentrate.  The 
average  unit-costs  of  a  number  of  plants  have  been  summarized  in  the 
following  tables,  which  will  indicate  the  probable  cost  of  a  complete 
equipment  of  flotation  machinery. 

FIRST  COST  OF  MINERALS  SEPARATION  MACHINES 
Tons  per  day  Cost  per  ton 

30  $30  to  $50 

50 25    "      45 

100 20    "      40 

250 15    "      35 

1000 12    "      25 

FIRST  COST  OF  PNEUMATIC  MACHINES 
Tons  per  day  Cost  per  ton 

30  $12  to  $20 

200 8    "      12 

1100 6    "        8 

5000 4    "        6 

FIRST  COST  OF  K.  &  K.  MACHINES 
Tons  per  day  Cost  per  ton 

80   $10  to  $15 

150 . 5    '         8 

In  these  tables  a  24-hour  day  is  assumed.  The  differences  in  the 
cost  of  machines  of  the  same  capacity  are  due  to  the  fact  that  a  given 
machine  has  a  much  greater  capacity  for  sand  than  for  slime,  and  it  is 
self-evident  that  the  lowest  cost  of  flotation  will  be  obtained  with  the 
easily  floated  granular  material  rather  than  with  colloidal  slime,  which 
requires  high  dilution.  Other  variations  in  the  above  data  are  due  to 
differences  in  materials  of  construction  and  the  care  with  which  the 
machines  are  built. 

Mill-units  of  more  than  1000  .tons  daily  capacity  are  rare,  conse- 
quently the  first  cost  of  the  larger  plants  is  not  much  smaller  than  that 
of  the  1000-ton  mills.  Usually  the  increase  in  capacity  brings  no  sav- 
ing. So  the  above  figures  will  have  to  be  used  with  caution,  as  they 
represent  the  averages  of  a  great  many  plants.  It  is  also  to  be  noted 
that  the  above  figures  cover  only  the  flotation  machinery  and  acces- 
sories, not  the  housing,  the  crushing  and  thickening  machinery,  or 
the  filters.  Considerable  differences  in  the  cost  items  are  found  ac- 


336  FLOTATION 

cording  to  the  materials  from  which  the  plants  are  built  and  it  is 
possible  to  put  up  a  flotation  unit  that  will  have  a  reasonable  life 
and  cost  much  less  than  the  lowest  figure  quoted. 

The  costs  of  a  few  equipments  are  as  follows : 

In  a  50-ton  unit  in  which  a  single  M.  S.  machine  was  used,  making 
concentrate  from  the  first  few  cells  and  middling  from  the  remainder, 
the  cost  ready  to  run  was  $2000,  while  the  factory  cost  of  the  machine 
was  estimated  to  be  $1500.  In  case  such  a  machine  is  to  be  used  with 
sub-aeration  the  blower  will  cost  an  additional  $250. 

A  250-ton  M.  S.  machine  will  cost  about  $4300  at  San  Francisco. 
In  one  plant  in  California  the  total  cost  of  the  mill  was  $115,000  and 
the  flotation  machine  of  the  above  capacity  was  only  a  small  part  of 
the  total.  Where  a  mill  is  already  running  and  flotation  is  added  the 
addition  is  usually  inexpensive  whereas  a  new  mill  will  cost  a  great 
deal  more.  The  grinding  and  crushing  machinery  alone  usually 
costs  many  times  the  amount  that  is  necessary  to  build  flotation 
machines. 

An  1100-ton  installation  was  made  in  a  copper-mill  at  the  follow- 
ing costs.  Three  14-box  M.  S.  rougher  machines  cost  about  $7000 
each  and  a  smaller  cleaner  unit  cost  $6000,  set  up. 

Turning  to  the  pneumatic  type  of  machine,  the  standard  Callow 
cell,  2  ft.  by  8  ft.,  has  cost  as  low  as  $100  in  wooden  construction  and 
$200  in  iron  construction.  Usually  the  iron  construction  will  cost 
$400  when  set  up  and  ready  for  shipment.  Such  a  cell  will  have  a 
capacity  of  from  25  to  50  tons  per  day.  The  total  cost  of  a  500-ton 
plant  with  grinding  machinery  and  filters,  as  given  by  H.  R.  Robbins 
for  the  Calaveras  plant,  was  about  $50,000,  the  machinery  being 
placed  in  an  old  mill-building.  The  National  plant,  at  Mullan. 
Idaho,  built  to  handle  the  same  tonnage  and  constructed  during  the 
winter,  with  a  fine  building  to  cover  it,  and  with  grinding  machinery 
sufficient  to  treat  extremely  hard  quartzite,  cost  $153.000.  These 
figures  show  how  hard  it  is  to  draw  comparisons  between  two  plants 
designed  to  concentrate  the  same  tonnage  of  ore  but  of  different  hard- 
ness and  physical  condition.  It  also  shows  how  unreliable  are  cost- 
data  when  conditions  are  not  specified.  The  individual  machines  in 
these  two  cases  probably  cost  about  the  same,  but  the  difficulties  of  con- 
struction and  the  amount  of  new  construction  made  the  difference. 

The  Southwestern  Engineering  Co.  advertises  the  cost  of  the  K. 
&  K.  machine  as  $800  for  wooden  construction  and  $1100  for  steel 
construction.  Such  a  cell  will  have  80  to  150  tons  daily  capacity. 

Janney  machines,  both  of  the  'straight  agitation'  and  the  'agita- 


COST    DATA  337 

tion  and  pneumatic'  types,  cost  about  $850  per  cell,  which  includes 
the  cost  of  the  individual  motors.  An  emulsifier,  five  roughers,  and 
two  cleaners  form  an  equipment  capable  of  treating  at  least  250  tons 
daily. 

THE  OPERATING  COST  has  varied  a  great  deal  according  to  the 
excellence  of  the  work  attained  in  the  individual  plants.  For  in- 
stance, a  flotation  equipment  treating  30  to  50  tons  of  slime  per  day 
in  a  small  mill  might  require  the  constant  attention  of  one  man  per 
shift,  while  the  great  plant  at  the  Inspiration  mine  calls  for  only  one 
man  to  each  four  800-ton  sections  (two  Mexican  helpers  are  also 
occasionally  used).  This  is  a  big  difference  in  labor  cost.  One  of  the 
things  to  be  done  in  the  near  future  is  to  develop  flotation  machines 
of  small  capacity  for  small  concentration  mills  and  so  designed  that 
they  will  require  only  occasional  attendance  from  the  table-man. 

The  tabulated  averages  of  operating  costs  at  a  number  of  plants 
are  given  herewith: 

OPERATING  COSTS  OF  M.  S.  MACHINES 


Tons  per  day 
25     

Flotation,  per  ton 
21-75c 

Total  milling 

$2  50 

100     

35 

1  30 

250             

28 

0  53 

500 

23 

1  03 

800 

0  58 

1100     

17 

2000     

0.30 

4000 

.    20 

0.30 

OPERATING  COST  OF  PNEUMATIC  MACHINES 


Tons  per  day 
60     

Flotation,  per  ton      Total 
15-75c                   $1  5 

milling 
0-2.50 

90 

11-50 

200 

10-35 

500 

9 

1  000 

7 

2  000 

6  75 

5.000 

5.30 

15,000     5.176  0.40-0.55 

It  was  hard  to  bring  all  of  the  above  figures  together  and  in  many 
cases  they  are  scarcely  comparable.  This  applies  especially  to  the 
total  cost,  as  the  data  have  been  collected  from  all  kinds  of  mills  some 
of  which  were  treating  complex  ores  that  required  complicated  flow- 
sheets, while  others  required  only  grinding  and  flotation.  However, 
the  flotation  operations  in  the  different  mills  do  not  differ  so  greatly 
and  the  figures  for  cost  on  the  flotation  alone  are  much  more  nearly 
comparable. 

At  the  Mount  Morgan  test-plant,  in  October,  1913,  the  flotation 


338  FLOTATION 

costs  were  as  follows,  covering  a  plant  in  which  83  tons  daily  was 
treated  by  an  M.  S.  machine : 

Per  ton,  cents 

Supervision   1.83 

Wages,  operating  3.69 

Power    , 2.96 

Supplies,  general   0.20 

Oil,  eucalyptus,  petroleum    10.20 

Maintenance    5.77 

Plant  and  general 1.25 

Sampling,  assaying  9.02 

Total    34.81 

A  250-ton  mill  operating  an  M.  S.  machine  in  a  Western  American 
mill,  gives  the  following  figures : 

Per  ton,  cents 

Power  and  supplies  21.6 

Labor     19.3 

Flotation  royalty 12.0 


Total    52.9 

The  Consolidated  Arizona  Smelting  Co.  has  given  out  particularly 
valuable  figures  of  cost  at  various  times.  The  mill  concentrates  a 
copper  ore  and  the  total  cost  on  the  500-ton  plant  is  $1.03,  including 
coarse  crushing  and  flotation  royalty.  The  following  are  the  items 
over  a  period  of  six  months,  from  July  to  December,  1915. 

Per  ton,  cents 

Wages    5.07 

Repairs   0.42 

Supplies    0.34 

Flotation-oil     3.90 

Water    0.62 

Power    5.04 

Lubricants     0.28 

Miscellaneous    .  .  0.18 


Total    15.85 

Overhead,  royalty,  etc 18.31 

34.16 

Itemized  according  to  operations  the  costs  in  this  mill  as  given  in 
another  estimate  are : 

Per  ton,  cents 

Crushing    25.07 

Grinding    32.95 

Tabling   19.92 

Flotation    ...  34.16 


Total  on  42,696  tons  $1.1210 

A  management  that  allows  the  publication  of  such  data  deserves  the 
thanks  of  the  profession. 

A  fourth  copper-mill  to  give  costs  is  the  Britannia  Mining  &  Smelt- 


COST    DATA  339 

ing  Co.,  which  operates  its  2000-ton  M.  S.  plant  at  a  cost  of  56c.  per 
ton  of  ore,  including  royalty,  but  expects  to  reduce  it  to  30  cents. 

Another  M.  S.  plant  is  that  of  the  Timber  Butte  Milling  Co.,  at 
Butte,  Mont.,  where  a  complex  zinc-lead  ore  is  treated.  This  mill 
requires  the  addition  of  acid  and  heat  to  obtain  good  flotation  of  the 
sphalerite.  This  increases  the  cost,  and  the  complicated  flow-sheet 
causes  a  total  milling  cost  of  $2  to  $2.25  per  ton  of  ore  in  a  500-ton  mill. 
The  flotation  items,  exclusive  of  royalty,  are  as  follows : 

Per  ton,  cents 

Heat 15 

Acid    08 

Power    03 

Oil     04 

Labor    '. 10 

Total     40 

Another  large  copper  concentrating  plant,  which  originally  found 
it  necsesary  to  heat  the  pulp  and  add  acid,  but  which  has  discontinued 
the  use  of  heat,  incurred  the  following  costs  on  an  1100-ton  scale : 

Per  ton,  cents 

Power  at  lOc.  per  hp.-day 3.0 

Oil  and  acid 4.7 

Attendance 1.7 

Repairs   1.5 

Miscellaneous    1.0 

Heating    5.0 

Total    17.0 

The  discontinuance  of  heating  lowers  the  cost  to  12c.  per  ton,  ex- 
clusive of  royalty. 

In  the  Missouri  lead-mills  30c.  per  ton  of  slime  is  allowed  for  pulp- 
thickening,  flotation,  and  filtering  of  the  concentrate,  in  units  of  500 
to  1000  tons  daily  capacity.  Most  of  these  mills  are  using  M.  S. 
machines. 

Turning  to  pneumatic  machines,  the  Calaveras  Copper  Co.,  as 
mentioned  in  the  paper  by  Robbins  (re-printed  elsewhere  in  this  book) 
gives  the  following  costs  on  a  192-ton  plant  for  crushing,  grinding, 
flotation,  and  filtering : 

Per  ton,  cents 

Power,  184  hp.  at  0.825c.  per  kw-hr 14.20 

Operating  labor,  10  shifts  at  $3.25 17.00 

Superintendence,  repairs,  extra  labor 10.20 

Supplies    9.86 

Total    51.40 

With  an  increased  capacity  of  500  tons  daily,  the  company  expects  to 
lower  the  cost  to  44.4c.  per  ton. 


340  FLOTATION 

At  the  sulphide  plant  of  the  Magma  Copper  Co.,  at  Superior, 
Arizona,  the  cost  of  flotation  by  Callow  machines  is  said  to  average 
about  33c.  per  ton  on  200  tons  mill-feed  daily.  The  total  milling 
cost  is  about  $1.11  per  ton,  of  which  22c.  per  ton  is  used  for  ore-sorting 
before  entering  the  grinding  system  and  19c.  per  ton  is  used  in  the 
table  department. 

At  one  small  mill,  in  the  Coeur  d'Alene  region,  treating  90  tons 
daily  of  a  galena  ore  in  a  home-made  pneumatic  machine,  flotation 
costs  lie.  out  of  a  total  milling  cost  of  35c.  per  ton. 

At  a  mill  in  the  North-west  treating  a  complex  zinc-lead  sulphide, 
differential  flotation,  calling  for  careful  operation  and  the  use  of  sul- 
phuric acid,  is  costing  as  follows  in  a  62-ton  plant: 

Per  ton,  cents 

Labor 24.25 

Flotation-oil     10.23 

Acid     • 3.44 

Thickening,  filtering,  blowers,  etc 33.96 

Loading  concentrate  3.71 

Total    76.59 

This  plant  uses  pneumatic  cells,  but  the  rigid  requirements  of  differ- 
ential flotation  make  necessary  the  use  of  excessive  power  and  air,  and 
considerable  acid  and  oil.  Besides  this  the  need  of  close  attention 
makes  the  labor  cost  rather  high  for  such  a  small  unit. 

In  the  same  district  another  plant  is  treating  a  simple  galena  ore. 
About  190  tons  of  slime  was  treated  per  day  by  pneumatic  flotation, 
which  has  since  been  displaced  by  a  mechanical  agitation  equipment 
which  gives  a  higher-grade  concentrate.  While  in  operation  the  costs 

were  as  follows : 

Per  ton,  cents 

Oil    0.83 

Power 2.94 

Lime    0.56 

Labor    1.67 

Total 6.00 

The  lime  was  used  for  settling  the  concentrate.  The  flotation  machines 
were  tended  by  the  table-man  who  gave  them  about  a  third  of  his 
time.  The  simple  ore  allowed  of  continuous  operation  without  much 
attention,  and  as  the  operation  was  not  a  delicate  one  the  cost  of  labor 
was  quite  low. 

At  one  large  copper-concentrating  plant  containing  a  unit  of  1100 
tons  the  estimated  cost  of  flotation  is  higher  owing  to  the  use  of  con- 
siderable oil  and  acid,  as  well  as  the  heating  of  the  solutions.  The 
itemized  costs,  when  the  oil  is  fed  into  the  tube-mill  and  the  Pachuca 
mixer  is  left  out  of  the  circuit,  are  as  foHows: 


COST    DATA  341 

Cents 

Power    1.5 

Oil,  acid    4.7 

Labor    1.7 

Repairs   1.0 

Miscellaneous    1.0 

Heating    5.0 

Total    15.0 

At  the  Miami  mill,  in  Arizona,  the  total  cost  of  operation  for  flota- 
tion in  a  5000-ton  plant  is  5.3c.  per  ton.  Neither  acid  nor  heat  is 
used  and  the  difference  would  make  about  the  same  relative  costs  as 
the  set  last  given. 

ROYALTIES.  It  was  to  avoid  the  payment  of  royalties  that  the 
Butte  &  Superior  Copper  Co.  took  up  Hyde's  method.  At  the  time 
they  commenced  operations  the  royalty  asked  was  about  25c.  per  ton 
of  ore.  Since  then  Minerals  Separation  has  modified  its  method  of 
asking  royalties  and  has  eliminated  the  flat  rate.  In  such  a  district  as 
Joplin  or  Flat  River,  in  Missouri,  the  total  cost  of  milling  is  rarely 
over  25c.  per  ton  and  to  pay  a  royalty  as  great  as  the  total  cost  of 
milling  seems  prohibitive.  The  contract  between  Minerals  Separa- 
tion and  the  Anaconda-Inspiration  companies  was  published  in  the 
Mining  and  Scientific  Press  of  September  16,  1916. l  It  discloses  a 
sliding  scale  of  royalty  ranging  from  12  cents  on  4000  tons  to  4  cents 
on  30,000  tons  or  more.  A  royalty  of  J  cent  per  pound  of  copper, 
but  not  less  than  12c.  per  ton  of  ore,  has  been  exacted  from  other 
mining  companies.  On  zinc  ores  the  royalty  is  based  on  the  old 
smelter  penalty,  being  at  the  rate  of  2c.  per  unit,  or  percentage, 
above  8%  zinc  in  the  concentrate,  so  that  on  a  50%  concentrate  it  is 
84c.  per  ton.  On  this  basis  the  Elm  Orlu  company,  at  Butte,  pays 
about  35c.  per  ton  of  crude  ore.  The  lead  schedule  is  the  same  as  that 
for  zinc.  On  precious-metal  ores  the  royalty  is  25c.  per  ounce  of  gold 
and  2^%  of  the  silver  value.  However,  all  these  royalties  are  de- 
pendent on  circumstances,  such  as  the  tonnage,  the  strength  of  the 
licensee,  and  the  ups  and  downs  of  the  patent  litigation,  which  one 
day  appears  to  have  established  the  M.  S.  people  where  they  can  do 
what  they  like  and  the  next  appears  to  divest  them  of  the  power  of 
exacting  any  tribute. 

POWER.  As  an  example  of  the  importance  of  the  power  question 
I  would  cite  the  instance  of  one  'porphyry-copper'  company  which 
reports  that  the  use  of  flotation  in  its  re-arranged  mill  will  call  for 
150%  of  the  former  power  used. 


•  See  also  editorial  on  'Flotation  Royalties'  in  the  same  issue. 


342  FLOTATION 

The  power  requirements  of  various  Minerals  Separation  machines 
have  been  determined  in  many  instances.  At  Inspiration  a  10-com- 
partrnent  rougher  machine  takes  100  hp.  for  840  tons  of  ore  and  two 
6-compartment  cleaners  use  75  hp.  This  totals  5.1  kw.-hr.  per  ton 
of  solid  passing  through  the  machine.  In  the  same  mill  the  pneu- 
matic machines  use  only  3.06  kw.-hr.  per  ton  of  solid.  The  M.  S. 
machines  are  of  the  Hebbard  type,  which  injects  air  under  the 
beaters  (sub-aeration)  and  hence  is  comparable  with  the  pneumatic 
machines.  The  comparison  is  evidently  not  in  favor  of  the  M.  S. 
machines.  However,  as  Laist  points  out,2  the  oil  can  be  added 
in  the  tube-mills  at  Inspiration  and  hence  the  pneumatic  cells  do  not 
require  Pachuca  or  other  mixers.  The  M.  S.  cells  are  good  mixers 
and  the  difference  in  power  consumption  between  the  pneumatic  and 
mechanical  systems  is  small  when  power  has  to  be  expended  on 
emulsification  of  the  flotation-oil  before  passing  to  flotation.  At 
Anaconda,  where  the  acid-oil  cannot  be  added  to  the  tube-mills,  the 
power  for  flotation  is  0.24  hp.  per  ton  of  daily  capacity  while  the 
Inspiration  pneumatic  machines  call  for  only  0.15  hp.  The  point  is, 
then,  that  by  adding  the  oil  in  the  tube-mills  the  power  can  be  cut 
down  as  much  as  40%  if  pneumatic  machines  are  used. 

Another  Hebbard  sub-aeration  machine  on  which  some  data  are 
available  is  that  of  the  Utah  Leasing  Co.,  at  Newhouse.  In  this 
plant  there  are  six  cells  without  sub-aeration  and  six  cells  of  the 
Hebbard  type.  The  capacity  is  rated  at  500  tons  daily  and  the  power 
used  is  75  hp.,  or  0.15  hp.  per  ton.  Actually  this  capacity  and  this 
figure  are  not  attained,  although  the  oiling  in  the  tube-mill  seems  to 
result  in  some  benefit.  The  air  required  for  the  six  Hebbard  cells 
of  24  by  24  in.  section  is  800  cu.  ft.  per  minute  at  5-lb.  pressure. 

At  the  Daly  West  mill,  at  Park  City,  Utah,  a  1 6-compartment 
M.  S.  machine  consumes  0.20  hp.  per  ton,  or  3.58  kw-hr.  per  ton  of 
solid. 

At  Anaconda,  some  good  data  have  been  collected.  On  the  Ana- 
conda slime  a  14-cell  M.  S.  machine  with  3  by  3  ft.  agitation-compart- 
ments and  8-in.  impellers  requires  75  hp.  and  has  an  economic 
capacity  of  130  tons  per  24  hours.  This  corresponds  to  the  use  of 
0.577  hp.  per  ton,  or  10.32  kw-hr.  per  ton  of  solid.  The  Anaconda 
sand  is  much  more  easily  treated  and  the  same  size  of  machine  can 
treat  400  tons  per  24  hours  with  an  expenditure  of  85  hp.,  or  0.212 
hp.  per  ton  or  3.81  kw-hr.  per  ton  of  solid.  The  total  power  con- 


2Bull.  119,  Am.  Inst.  M.  E.,  Nov.,  1916,  p.  1880. 


e   COST  DATA  343 

sinned  in  milling  at  Anaconda  is  0.96  hp.  per  ton  capacity  or  17.2 
kw-hr.  per  ton  of  solid. 

At  the  Consolidated  Arizona  mill,  at  Humboldt,  an  11-cell  M.  S. 
machine  is  said  to  be  operating  with  2.61  kw-hr.  per  ton  of  solid. 
This  is  much  lower  than  the  power  consumption  of  other  M.  S. 
machines. 

At  the  Old  Dominion  mill,  at  Globe,  Arizona,  the  power  consump- 
tion in  a  16-cell  M.  S.  machine  is  given  as  8.6  kw-hr.  per  ton  of  solid, 
the  slime  being  a  difficult  one  to  treat  by  flotation.  This  is  23.5% 
of  the  total  mill-power. 

As  intimated  above,  the  power  consumption  of  a  pneumatic  equip- 
ment is  usually  smaller  than  in  a  mechanical  agitator.  The  Inspira- 
tion mill  contains  largely  pneumatic  machines  and  the  power  con- 
sumption, as  stated  above,  is  3.06  kw-hr.  per  ton  of  solid.  The  total 
mill-power  is  16.07  kw-hr.  per  ton.  Hence  flotation  consumes  19% 
of  the  total. 

At  Miami  the  power  used  in  Callow  cells  amounts  to  2.88  kw-hr. 
per  ton  of  solid  and  the  total  mill-power  is  only  11.36  to  12.53  kw-hr. 
per  ton  of  solid,  depending  upon  which  season's  reports  are  used  in 
making  the  calculation.  It  is  of  interest  to  note  that  the  air  is  used 
under  5-lb.  pressure  and  that  about  8.9  cu.  ft.  per  minute  passes 
through  every  square  foot  of  canvas  bottom.  There  are  sixty  2  by  9  ft. 
cells  in  this  plant. 

At  the  Silver  King  Coalition  mill,  at  Park  City,  Utah,  5  hp.  is 
needed  to  supply  air  for  each  standard  8  by  2  ft.  Callow  cell.  The 
pressure  is  5  Ib.  and  the  air  consumption  per  square  fcot  of  canvas  is 
7.45  cu.  ft.  per  minute. 

At  the  Hunter  mill  at  Mullan,  Idaho,  5.6  hp.  per  Callow  cell  is 
needed. 

At  the  Calaveras  plant  at  Copperopolis,  California,  the  air  is 
used  at  5.5  Ib.  per  sq.  in.  and  the  consumption  is  8.2  cu.  ft.  per  square 
foot  of  canvas,  per  minute.  The  total  mill  uses  184  hp.  on  192  tons  of 
ore  per  24  hours,  or  0.96  hp.  per  ton,  or  17.2  kw-hr.  per  ton  of  solid 
milled. 

The  pneumatic  plant  in  the  Magma  mill  at  Superior,  Arizona,  uses 
80  hp.  for  the  flotation  of  200  tons  of  ore,  or  7.15  kw-hr.  per  ton  of 
solid — a  rather  high  figure  for  a  pneumatic  plant.  The  total  power 
consumed  in  this  plant  amounts  to  22.8  kw-hr.  per  ton  of  solid,  the 
power  used  on  the  concentrating  machinery  amounting  to  as  much 
as  that  used  for  flotation  and  the  power  for  grinding  amounting  to 
165%  of  that  used  for  flotation. 


344  FLOTATION 

The  power  consumption  by  Janney  machines  is  usually  not  given 
out  by  those  using  them,  as  it  is  rather  high  owing  to  the  intense 
stirring  effects  obtained  by  their  peculiar  design  and  their  high  rate 
of  speed.  I  am  informed  that  in  one  plant  where  five  cells  in  series 
receive  200  tons  of  feed  daily,  the  total  power  consumed  is  about 
75  hp.,  or  6.26  kw-hr.  per  ton  of  solid.  This  is  known  to  be  some- 
what high  and  it  is  believed  that  the  figure  can  easily  be  lowered  to 
5  or  6  kw-hr. 

The  K.  &  K.  machine  has  made  some  remarkable  records  in  power 
consumption  and  is  at  present  being  sold  on  the  statement  that  it 
uses  8  to  10  hp.  per  80-150  tons  of  feed.  This  means  1.2  to  1.6  kw-hr. 
per  ton  of  solid. 

Summing  up,  it  would  seem  that  other  things  being  equal,  the 
power  consumption  of  mechanical  and  of  pneumatic  machines  is 
about  the  same  when  mixing  of  the  oil  does  not  take  place  previously 
in  a  tube-mill  or  similar  grinding-machine.  In  case  it  is  possible 
to  add  the  oil  to  tube-mills  the  pneumatic  system  presents  a  saving 
of  powrer.  For  ores  tfiat  require  an  extreme  degree  of  agitation,  the 
Janney  machine  has  probably  proved  better  than  any  others,  although 
it  has  a  rather  high  power-consumption.  The  dark  horse  in  flota- 
tion machinery,  as  far  as  low  power-consumption  is  concerned,  is  the 
K.  &  K.,  for  which  very  low  power-consumption  is  claimed. 

Tabulating  what  I  believe  to  be  the  best  work  demonstrated  by 
the  various  types  of  machines  in  use,  the  following  table  of  power- 
consumption  has  been  prepared : 

Per  ton  of  solid 
kw-hr. 

Janney  machines  (with  air-baskets)    5.0  to  6.0 

Mechanical  Minerals  Separation   4.0    "    5.0 

Sub-aeration  Minerals  Separation    3.5 

Pneumatic    (Callow,    Inspiration)     3.0 

K.    &   K.  .   2.0 


CONTROL    OF    ORE-SLIME  345 


THE  CONTROL  OF  ORE-SLIME 

BY  OLIVER  C.  RALSTON 
(Prom  the  Engineering  and  Mining  Journal  of  April  29,  1916) 

Not  so  many  years  ago  it  was  an  accepted  axiom  among  mill-men 
that  "you  must  not  make  slime  in  your  mill  if  you  wish  to  saye  the 
mineral/'  But,  sadly,  whenever  men  put  ore  through  crushing 
machinery  some  'rock  flour'  was  inevitably  formed,  and  slime  soon 
came  to  be  considered  a  necessary  evil.  For  years  the  slimes  were  run 
to  waste  from  concentrating  mills  for  the  simple  reason  that  there 
was  no  known  way  of  concentrating  the  valuable  minerals  in  them. 
If  the  slimes  were  rich  enough  to  be  smelted  as  a  whole,  they  were  so 
treated,  but  this  was  rarely  the  case,  and  even  then  much  of  the  fine 
material  went  into  the  flue-dust.  Those  were  the  days  when  we  knew 
little  more  about  handling  flue-dust  than  we  did  about  concentrating 
slime. 

Some  of  the  first  slimes  to  yield  to  any  treatment  were  those  from 
free-milling  ores  in  which  some  of  the  gold  could  be  amalgamated, 
although  'flour-gold'  was  soon  recognized  as  a  source  of  loss.  The 
ancient  buddle  recovered  galena  to  some  extent  from  slime  containing 
it,  and  occasionally  it  did  fair  work  on  the  recovery  of  other  slimed 
sulphides.  The  savings  were  rarely  large,  and  it  was  a  case  of  grab 
all  you  can.  The  development  of  the  Wilfley  table  brought  about  the 
invention  of  slime-tables,  on  which  recoveries  were  better,  but  still 
left  much  to  be  desired.  Vanners,  likewise,  have  never  made  recov- 
eries as  high  as  desired. 

For  a  time  after  the  introduction  of  slime-tables  we  were  prone  to 
pat  ourselves  on  the  back  and  say  that  we  now  had  machinery  for  the 
treatment  of  all  sizes  of  ore.  At  one  end  of  the  line  we  had  bull-jigs, 
and  at  the  other  end  were  vanners  and  tables.  After  such  pompous 
talk  it  is  little  wonder  that  many  mill-men  became  timid  about  pub- 
lishing tailing-assays.  Every  mill-man  knew  that  in  spite  of  the  best 
work  that  he  was  able  to  get  out  of  his  slime-handling  machinery,  he 
was  getting  lower  extractions  than  were  desirable.  It  was  only  too 
well-known  that  we  were  still  afraid  to  make  slime  in  a  mill  and  that 
a  classification  of  crushing  machinery  was  made  according  to  whether 


"Communicated  by  D.  A.  Lyons,  metallurgist  in  charge  of  Salt  Lake  station 
in  co  operation  with  the  Metallurgical  Research  Department  of  the  University 
of  Utah.  O.  C.  Ralston,  metallurgist,  United  States  Bureau  of  Mines. 


346  FLOTATION 

any  particular  machine  in  question  made  slime  or  not.  Further, 
stage-crushing  was  developed  in  order  that  a  minimum  of  slime  might 
be  produced. 

Imagine  the  distrust  with  which  the  proposals  of  the  cyanide-men 
were  received  when  it  was  found  that  some  ores  would  have  to  be 
slimed  in  order  that  their  gold  might  be  liberated  for  cyanidation. 
As  cyaniding  developed  into  the  stage  of  all-sliming,  it  broke  every 
supposed  rule  of  the  art.  The  procedure  seemed  suicidal  when  the 
experiences  of  concentrating  mills  were  considered.  Thanks  to  the 
fact  that  gold  had  a  fixed  price  and  could  always  be  sold,  no  matter  in 
what  amount  it  was  produced,  the  cyanide-men  went  ahead  undaunted 
and  developed  new  machinery.  We  have  seen  settling,  classifying, 
decanting,  thickening,  agitating,  filtering,  and  grinding  machinery 
develop  to  a  stage  where  slime  can  be  made  and  treated  cheaply. 

These  were  all  mechanical  methods  and  were  absolutely  necessary 
before  we  could  turn  to  the  chemical  or  semi-chemical  methods  of 
controlling  slime.  We  have  seen  cyanide-men  use  lime  as  a  flocculat- 
ing agent  for  making  slime  settle  faster,  and  flotation  has  recently 
been  added  to  the  methods  by  which  we  can  control  slime.  We  have 
found  that  we  can  separate  sulphide  minerals  from  most  slimes  by 
flotation  and  with  recoveries  much  more  nearly  perfect  than  by  any 
of  the  older  machinery.  In  spite  of  all  the  appreciation  of  this  new 
process,  we  have  not  taken  sufficient  stock  of  its  potentialities. 

But  the  old  fear  of  slime  has  been  slow  to  die,  and  there  have  been 
doubters  that  have  said  that  like  all  other  new  methods  the  promise  of 
flotation  will  be  greater  than  its  fulfillment.  This  verdict  must  be 
withheld  for  a  time,  as  we  have  seen  flotation  expand  its  field  wonder- 
fully in  the  past  two  years.  We  find  that  it  is  not  only  possible  to  float 
sulphide  minerals,  but  also  metals  such  as  gold,  silver,  and  copper, 
while  it  is  easy  to  alter  oxidized  minerals  into  such  a  condition  that 
they  will  float.  Further  than  this,  it  seems  possible  to  float  one  sul- 
phide mineral  in  preference  to  another — differential  flotation. 

The  significance  of  these  facts  is  beginning  to  force  itself  home,  and 
people  all  over  the  mining  world  are  beginning  to  take  stock  of  the 
ores  that  have  resisted  treatment  by  ordinary  methods.  Low-grade 
and  complex  ores  are  becoming  popular,  for  we  are  beginning  to  fee] 
confident  that  we  can  grind  any  ore  until  the  particles  of  the  indi- 
vidual minerals  are  liberated  mechanically  from  one  another,  and 
after  that  we  can  separate  them  by  flotation  or  some  other  slime- 
process.  The  War  has  stimulated  mining  in  the  United  States  to  such 
an  extent  that  some  of  these  new  methods  have  been  put  directly  into 


CONTROL    OF  .ORE-SLINK  347 

practice.  A  movement  of  some  magnitude  has  been  made  toward  the 
dumps  and  stope-fillings  of  past  generations.  This  is  as  good  as  the 
opening  of  new  mines,  except  that  the  metallurgist  reaps  the  reward. 

It  is  the  purpose  of  this  paper  to  point  out  a  few  other  methods  that 
seem  to  promise  well  in  the  treatment  of  slimes  and  to  present  the 
results  of  some  experiments  in  settling  such  mill-products.  The  object 
of  these  experiments  was  to  gain  control  of  the  settling  of  slimes  in 
such  a  manner  that  they  could  be  caused  to  settle  faster,  slower,  not 
at  all,  or  else  to  make  one  particular  set  of  minerals  settle  out  of  a 
suspension  while  another  set  would  remain  suspended.  This  work 
met  with  notable  success  except  in  differential  settling,  where  only 
incomplete  separation  was  attained  with  one  ore. 

All  of  this  work  has  been  based  more  or  less  on  colloid  chemistry, 
and  it  had  been  my  original  purpose  to  discuss  thoroughly  the  prin- 
ciples of  colloid  chemistry  involved.  The  publication  of  the  series  of 
articles  on  'Colloids  in  Ore  Dressing'  by  E.  E.  Free  makes  this  un- 
necessary and  allows  this  paper  to  be  shortened.  I  am  obliged  to  Mr. 
Free  for  the  privilege  of  perusing  his  papers  in  advance  and  for  the 
opportunity  to  publish  my  paper  coincidently  with  his.  Most  of  his 
ideas  have  my  hearty  endorsement,  and  this  paper  may  be  looked  upon 
as  a  verification  of  many  of  the  principles  he  has  explained.  I  have 
already  discussed  the  theory  of  notation  from  the  colloid-chemical 
standpoint1  as  well  as  a  colloid-chemical2  explanation  of  the  adsorp- 
tion of  gold  from  cyanide  solutions  by  charcoal  and  other  carbon- 
aceous materials. 

My  recent  work  has  shown  that  suspensions  of  fairly  coarse  ma- 
terial will  react  like  those  colloidal  sols  known  as  suspensoids,  even 
though  they  settle  completely  in  a  short  time.  It  is  possible  to  greatly 
affect  the  rate  of  settling  of  ore-slimes  by  the  addition  of  relatively 
small  amounts  of  the  proper  substances,  which  are  also  known  to  affect 
recognized  colloids  in  a  like  manner.  Confirmation  of  the  effects  pro- 
duced can  be  found  in  current  literature,  especially  in  recent  patents. 

As  an  example  we  may  take  certain  patents  of  B.  Schwerin3,  in 
which  a  method  of  separating  magnetic  particles  from  slime  is  set 
forth.  Schwerin  depends  upon  suspending  the  slime  in  water  and 
deflocculating  it  with  the  proper  deflocculating  agent  in  order  to  break 
up  the  little  groups  of  material  into  individual  particles  so  that  the 


i'Why  Do  Miners  Float?'  0.  C.  Ralston,  M.  &  S.  P.,  Vol.  CXI,  p.  623 
(1915). 

^'Precipitating  Action  of  Carbon  in  Cyanide  Solutions,'  M.  &  S.  P.,  Vol. 
CXI,  p.  77  (1915). 

«U.  S.  Pat.  No.  1,063,893  of  1913  and  British  Pat.  No.  19,313  of  1914. 


348  FLOTATION* 

introduction  of  a  magnet  will  remove  only  the  magnetic  particles.  He 
speaks  of  the  deflocculated  ore  as  being  in  a  sol  condition,  this  being  a 
colloidal  term  that  assumes  that  a  colloid  is  in  such  a  condition  that 
it  will  not  settle  out  of  the  suspending  liquid.  For  my  purposes  the 
term  'deflocculated'  (also  accepted  by  colloid  chemists)  is  better,  as 
the  only  assumption  in  the  word  is  that  the  floccules  usually  present 
in  ore-slime  are  caused  to  separate  into  their  individual  constituents, 
even  though  these  individual  particles  are  still  heavy  enough  to  settle 
out  of  the  water  on  standing.  Deflocculation  leaves  the  magnetic 
particles  individually  suspended  so  that  they  can  be  removed  by  means 
of  magnets  with  a  minimum  of  entrainment  of  non-magnetic  particles. 
Deflocculation  is  obtained  by  use  of  electrolytes  of  basic  nature  (con- 
taining an  excess  of  hydroxyl  ions)  when  the  slime  is  made  up  mostly 
of  particles  carrying  a  negative  electric  charge.  Electrolytes  of  an 
acid  nature  (containing  excess  of  hydrogen  ions)  will  likewise  defloc- 
culate  a  slime  whose  particles  are  positively  charged.  Most  ore-min- 
erals are  negatively  charged,  and  hence  the  effect  of  alkaline  electro- 
lytes like  sodium  hydroxide  in  making  many  slimes  settle  more  slowly, 
by  deflocculating  them,  is  a  well-known  observation. 

The  reality  of  the  electric  charges  on  suspended  particles  of  matter 
in  liquids  can  be  demonstrated  by  trapping  some  of  the  slime  between 
two  microscope  slides  and  applying  a  direct  current  of  110  volts  to 
the  two  ends  of  the  arrangement,  taking  care  that  space  is  afforded  for 
the  gases  evolved  by  electrolysis  in  such  a  manner  that  the  movement 
of  the  particles  will  not  be  affected  by  these  bubbles  of  gas.  By 
observing  the  particles  with  the  microscope,  they  will  be  seen  to  move 
as  the  potential  is  applied,  and  their  motion  reverses  when  the  current 
is  reversed.  Knowing  the  polarity  of  the  current  applied,  we  find 
that  the  particles  moving  toward  the  positive  electrode  must  be  nega- 
tive and  the  negative  electrode  is  the  distinction  of  the  positively 
charged  particles.  An  improved  miniature  electric  cell  of  this  type 
has  been  used  in  my  laboratory  for  a  study  of  the  charges  on  the  par- 
ticles of  material  that  were  tested  for  flotation  in  a  testing-machine. 

The  colloid  chemists  explain  deflocculation  somewhat  as  follows: 
Suspended  colloids  have  been  found  to  possess  the  power  of  adsorbing 
dissolved  substances  and  ions  from  solution  in  amounts  that  vary  with 
the  different  substances  involved.  Water  is  somewhat  ionized,  and 
substances  that  are  negatively  charged  when  suspended  in  water,  or 
even  in  contact  with  it,  have  adsorbed  more  hydroxyl  ions  than  hydro- 
gen ions,  and  as  the  hydroxyl  ions  are  negatively  charged,  the  particles 
show  a  negative  charge.  The  amount  of  the  electro-static  charge  has 


CONTROL    OF    ORE-SLIME  349 

been  measured  to  be  as  low  as  the  charge  on  a  single  monovalent  ion 
and  as  large  as  that  on  at  least  a  thousand  ions,  for  several  typical 
colloids.  If  an  alkali  is  added  to  the  water,  the  excess  of  hydroxyl  ions 
due  to  the  alkali  can  be  further  adsorbed  by  such  a  negatively  charged 
particle,  and  it  will  repel  other  similarly  charged  particles  with  greater 
force ;  or  in  case  they  are  adhering  together  in  floccules,  they  become 
so  highly  charged  that  they  break  apart  and  the  result  is  defloccula- 
tion.  Varying  dilutions  of  alkali  cause  various  numbers  of  ions  to  be 
adsorbed  onto  the  surfaces  of  the  suspended  particles,  giving  them 
greater  or  less  electric  charges  and  causing  higher  or  lower  degrees  of 
flocculation.  The  laws  of  adsorption  are  obscure,  and  we  do  not  know 
why  suspended  particles  adsorb  ions  or  dissolved  substances  onto 
their  surfaces  and  hold  them  so  tightly.  It  is  equally  hard  to  explain 
why  some  particular  ions  are  adsorbed  more  than  others.  However, 
the  phenomena  have  been  well-enough  classified  for  us  to  use  these 
various  effects  intelligently. 

Returning  now  to  Schwerin's  patents,  he  describes  an  experiment 
in  which  1950  grammes  of  raw  ore  containing  23.5%  iron  was  pulver- 
ized in  the  wet  state  until  all  the  particles  would  pass  a  screen  with 
i  mm.  opening,  and  reduced  to  a  slime  by  water.  To  this  was  added 
20  gm.  of  a  normal  solution  of  caustic  soda,  which  deflocculated  the 
components.  Part  of  the  ore  remained  in  suspension,  and  the  other 
part  settled  out.  This  latter  part  was  led  to  a  magnetic  separator  (of 
the  Grondal  wet  type)  in  which  the  magnetic  portion  was  separated 
from  the  non-magnetic.  There  resulted  175  gm.  of  magnetic  material 
containing  49.6%  iron  and  15.6%  sludge.  The  non-magnetic  product 
amounted  to  775  gm.  with  9%  iron  and  87%  sludge.  In  the  suspen- 
sion, which  was  not  taken  to  the  magnetic  separator  and  whose  largest 
grains  were  less  than  V15  mm.  diameter,  a  further  settlement  occurred 
after  some  time,  amounting  to  520  gm.  containing  37.9%  iron  and 
29%  sludge,  while  480  gm.  of  clay  material  remained  in  suspension. 
The  175  gm.  of  magnetic  concentrate,  together  with  the  520  gm.  of 
settled  material,  form  concentrate  weighing  695  gm.  of  40.6%  iron 
and  25.6%  sludge.  This  amounts  to  an  extraction  of  61.4%.  While 
the  work  is  not  particularly  good,  it  indicates  possibilities.  Further 
investigation  of  this  process  is  certainly  warranted. 

Another  magnetic  process  that  works  with  suspended  slimes  is  the 
Murex,  owned  by  the  Murex  Magnetic  Co.,  of  London,  and  protected 
by  U.  S.  Pat.  No.  933,717  of  1909,  959,239  of  1910,  and  996,491  of 
1911,  as  well  as  British  Pat.  No.  25,369  of  1911  and  174  of  1915. 
These  patents  were  taken  out  by  A.  A.  Lockwood  and  assigned  to  the 


350  FLOTATION 

Murex  Magnetic  Co.  The  process  depends  upon  the  fact  that  certain 
oils  adhere  to  particles  of  sulphide  minerals  when  suspended  in  water, 
in  preference  to  adhering  to  the  gangue-particles.  The  flotation 
process  depends  upon  the  same  fact,  though  utilized  in  a  different  way. 
In  this  case  a  finely  ground  magnetic  material,  such  as  iron  filings  or 
ground  magnetite  or  pyrrhotite,  is  mixed  into  the  oil  before  it  is  mixed 
with  the  ore,  and  when  the  oil  adheres  only  to  the  sulphide  minerals 
we  find  that  these  are  receiving  a  coat  of  '  magnetic  paint. '  By  using  a 
magnetic  separator  adapted  to  slime  separation,  such  as  the  Grondal 
machine,  the  sulphide  particles  are  lifted  out  of  the  pulp,  away  from 
the  non-magnetic  gangue.  Material  of  sizes  hardly  regarded  as  slime, 
such  as  particles  2  or  3  mm.  diameter,  can  also  be  treated  in  this  way. 
The  process  has  been  tested  at  the  Bergwerks-Wohlfahrt,  near  Claus- 
thal,  in  the  Harz  mountains  of  Germaii}r,  as  Avell  as  at  the  Whimwell 
mine  in  Australia.  Fairly  satisfactory  results  have  been  obtained, 
though  occasionally  baffling  difficulties  were  encountered.  The  mag- 
netic paint,  which  is  made  up  of  oil-gas  tar  mixed  with  twice  its  weight 
of  finely  ground  cast-iron  (any  animal,  mineral,  or  vegetal  oil  can  be 
used,  or  even  a  fatty  acid,  soap,  or  other  such  material),  is  applied  in 
a  horizontal  rotating  cylinder  resembling  a  tube-mill  except  that  it  is 
lined  with  blocks  of  wood  set  on  end.  The  mill  contains  iron  or  lead 
shot  and  pebbles,  and  the  discharge  is  preferably  at  the  periphery  of 
the  end.  The  metal  balls,  which  are  about  J  in.  diameter,  become 
coated  with  the  paint,  which  they,  in  turn,  rub  onto  the  surfaces  of  the 
ore-particles.  The  function  of  the  pebbles  is  to  prevent  formation  of 
granules  of  oiled  minerals  or  any  other  lumps  or  agglomerations,  and 
to  prevent  the  shot  from  sticking  together.  It  is  best  to  give  the  peb- 
bles a  coating  of  paint  before  they  are  put  into  the  mill.  The  shot  are 
inspected  from  time  to  time,  and  it  has  been  found  that  so  long  as  they 
are  well-coated,  the  process  works  satisfactority.  In  case  the  ore  re- 
quires grinding,  the  operation  can  be  carried  on  in  an  ordinary  tube- 
mill. 

Some  difficulty  was  caused  by  the  tendency  of  the  ground  magnetite 
or  other  material  to  leave  the  oil  and  go  into  the  water.  One  of  the 
patents  already  mentioned  covers  a  method  of  preventing  this  loss  of 
the  magnetite  by  using  additional  agents  with  the  oil  when  the  mag- 
netic paint  is  made  up.  When  using  saponifiable  oils,  all  that  is  neces- 
sary is  the  use  of  any  sulphate,  chloride,  sulphide,  hydrate,  or  other 
salt  soluble  in  the  oil  or  which  forms  insoluble  soaps  with  the  oil.  In 
case  the  oil  used  is  a  mineral-oil  that  will  not  saponify,  it  will  require, 
in  addition  to  the  salt,  a  small  amount  of  soap  or  saponifiable  oil.  A 


CONTROL    OF    ORE-SLIME  351 

small  amount  of  a  solution  containing  1  to  5%  of  alum,  mixed  with 
the  oil,  has  been  found  to  do  good  work. 

With  some  ores  it  is  found  that  an  acid  solution  works  best  and 
with  others,  alkaline  solutions.  As  a  mineral  froth  does  not  have  to 
be  formed,  this  process  can  work  through  a  wider  range  of  solutions 
than  can  the  flotation  process.  The  plant  at  Wohlfahrt  used  a  neutral 
solution  and  treated  a  galena  ore  containing  10%  lead,  while  the 
Whimwell  plant  used  an  alkaline  solution  and  treated  a  copper  ore 
containing  sulphides  and  carbonates. 

,  The  Wohlfahrt  plant  was  discussed  by  James  M.  Hyde.4  The  plant 
is  a  10-ton  experimental  one  and  is  said  to  have  done  such  satisfactory 
work  that  other  operators  have  been  considering  the  introduction  of 
the  process.  A  mixture  of  paraffine  oil,  pitch,  resin,  and  finely  ground 
magnetite  is  used.  A  feed  of  9000  kg.  of  ore  per  day  requires  20  kg. 
of  paraffine  oil,  40  kg.  of  brown  pitch,  and  0.2  kg.  of  resin,  mixed  with 
72  kg.  of  finely  ground  magnetite.  The  total  cost  of  running  this 
process  is  about  59c.  per  ton  of  ore.  The  feed  averages  6  to  8%  lead 
and  the  concentrate  62%  lead  and  1.13%  silver.  The  tailing  averages 
1.1%  lead.  Mr.  Hyde  asserts  that  the  American  equivalents  of  the 
oily  materials  used  will  cost  less  in  America  than  they  do  in  Germany. 

The  Whimwell  plant  was  forced  to  do  a  great  deal  of  experimental 
work  and  always  seemed  to  have  good  chances  of  success,  although 
there  were  unknown  adverse  conditions  that  were  never  completely 
mastered.  The  addition  of  caustic  soda  to  the  pulp  seemed  to  be  the 
best  general  corrective  whenever  anything  went  wrong,  but  so  far  as 
I  have  been  able  to  learn,  the  plant  left  many  things  to  be  desired.  I 
do  not  know  what  has  been  the  fate  of  this  and  of  the  Wohlfahrt  plant 
since  the  War  started. 

The  underlying  theory  of  the  process  is  undoubtedly  much  the 
same  as  that  of  the  flotation  process,  wherein  certain  minerals  are 
coated  with  oils  while  others  remain  uncoated.  In  fact,  it  has  not 
been  proved  that  the  Murex  process  will  treat  any  ore  that  the  flota- 
tion process  cannot  treat  unless  we  except  Hyde 's  statement  that  under 
proper  conditions  it  is  possible  to  treat  lead  carbonate  by  this  process. 

In  this  connection  Hyde  probably  had  in  mind  U.  S.  Pat.  No. 
996,491,  taken  out  by  Lockwood  and  assigned  to  the  Murex  Magnetic 
Co.,  in  which  is  given  a  method  of  applying  the  process  to  the  con- 
centration of  oxides  and  carbonates.  This  consists  of  the  use  of  a 
soluble  alkaline  sulphide  in  solution  to  form  a  film  of  metallic  sulphide 


4'The  Murex  Process  in  a  German  Works,'  James  M.  Hyde,  M.  &  S.  P. 
June  6,  1914. 


352  FLOTATION 

over  the  surface  of  the  carbonate  particle  by  reaction  with  the  same. 
Thus  the  reaction  with  the  lead  carbonate  of  an  ore  is  as  follows : 
PbCO:!  -f  Na,S  =  PbS  +  Na2CO, 

Lockwood  gives  two  examples  of  the  method  of  working.  A  100-lb. 
lot  of  ore  containing  carbonate,  phosphate,  and  chloride  of  lead  was 
crushed  to  pass  a  24-mesh  screen  and  then  suspended  in  80  Ib.  of  water. 
To  this  was  added  4  Ib.  of  finely  ground  magnetite  in  2  Ib.  of  Texas 
residuum-oil.  After  agitation  for  about  10  minutes,  a  solution  con- 
taining about  3  oz.  of  potassium  sulphide  was  added.  A  film  of  lead 
sulphide  was  formed  on  the  oxidized  lead  minerals,  and  they  were 
successfully  coated  with  magnetic  paint  ready  for  separation  in  a 
magnetic  separator.  The  second  example  is  of  the  sulphide-filming 
of  a  carbonate  ore  of  copper — likewise  successful. 

As  the  sulphide-filming  of  carbonate  ores  of  lead  and  copper  is  now 
meeting  with  considerable  success  in  the  flotation  process,  it  cannot 
be  said  that  the  Murex  process  has  any  field  that  is  particularly  its 
own.  In  fact,  there  does  not  seem  to  be  anything  the  Murex  process 
can  do  which  the  flotation  process  will  not  do.  The  greater  uncertainty 
of  successful  operation  of  the  Murex  process,  as  wrell  as  the  greater 
amounts  of  oils  and  chemicals  used,  seems  to  make  it  less  desirable. 

Lockwood5  has  also  presented  a  method  of  treating  the  fine  of  mixed 
materials  in  order  to  avoid  having  to  grind  it  further.  Middlings  of 
galena  and  sphalerite  can  be  treated  with  a  solution  of  a  caustic  alkali 
and  silicate  of  soda,  with  the  result  that  the  galena  and  sphalerite 
separate  along  cleavage-lines  without  the  need  of  further  crushing. 
Supposedly  this  is  due  to  the  tendency  of  sodium  hydrate  and  silicate 
to  disperse  a  suspension  of  negatively  charged  particles.  The  increase 
in  degree  of  dispersion  of  clays  by  the  use  of  these  chemicals  is  fairly 
well  known.  After  freeing  the  galena  and  sphalerite  in  this  way,  they 
can  be  separated  on  a  table  or  on  a  vanner.  He  proposes  the  same 
method  for  the  tabling  of  mixed  zinc-lead  flotation  concentrates. 

SEPARATION  BY  USE  OF  SODIUM  HYDROXIDE 

Concentrate  Middling 

Size  Lb.  Pb,  %  Zn,  %  Lb. 

On  60  103.5      \  7fi  8  q  Q  /  43.5 

On  80  172.0      /  I  36.5 

COMPARISON  BY  USING  PURE  WATER 

Size  Lb.  Pb,  %  Zn,  %  Lb. 

On  60  88    I  79  A  K  f    130 

On  80  134    /  (68 

Lockwood  quotes  two  tests  that  were  run  on  two  tons  of  ore  from 


BIT.  S.  Pat.  No.  956,381  of  April  26,  1910. 


CONTROL    OF    ORE-SLIME  353 

the  Broken  Hill  Proprietary  mine.  The  ore  was  crushed  to  about 
40-mesh  and  divided  into  two  lots.  One  lot  of  2240  Ib.  was  treated 
with  500  Ib.  of  a  solution  containing  5%  of  caustic  soda  and  1%  of 
sodium  silicate.  After  agitating  for  30  minutes,  the  pulp  was  fed 
onto  shaking  screens,  and  the  material  remaining  on  the  60  and  the 
80-mesh  screens  was  run  over  vanners.  The  results  are  shown  above. 
With  the  other  lot  of  2240  Ib.  the  same  conditions  were  observed  except 
that  pure  water  was  used  on  the  ore  instead  of  the  dispersing  agents. 
The  results  are  tabulated  for  comparison. 

Lock  wood  examined  the  middlings  in  each  instance  and  found  that 
in  the  case  of  the  dispersed  pulp  they  seemed  to  be  made  up  of  free 
crystals  of  galena  and  sphalerite,  while  the  middling  from  the  test  in 
water  seemed  to  be  a  true  middling,  containing  composite  particles  of 
the  two  sulphides  that  required  further  grinding.  Just  how  he  did 
this  is  not  mentioned,  and  I  am  inclined  to  doubt  that  true  middlings 
were  actually  broken  up  by  the  sodium  compounds.  It  is  thoroughly 
possible  that  floccules  containing  both  sulphides  could  be  dispersed  by 
the  sodium  salts  and  that  it  was  hence  easier  to  get  a  good  clean  tabling 
test  on  this  account.  The  idea  certainly  merits  further  investigation. 

One  particularly  interesting  method  of  controlling  slimes  of  all 
descriptions  has  been  described  by  Count  Botho  Schwerin,  a  citizen  of 
Germany,  in  a  number  of  patents0.  Schwerin  has  been  instrumental 
in  the  application  of  colloid  chemistry  to  many  problems,  among  which 
are  the  dehydration  of  peat  and  other  organic  materials,  the  purifica- 
tion of  clay,  the  production  of  special  ceramics,  and  the  concentration 
of  various  ores.  It  has  been  found  that  many  suspensions  of  clays  with 
their  impurities  can  be  purified  by  utilizing  the  fact  that  particles  of 
colloids,  when  suspended  in  water,  will  migrate  toward  one  or  the 
other  of  two  electrodes  introduced  into  the  suspension,  depending 
upon  the  sign  of  the  electric  charge  carried  by  the  particles.  Direct 
current  is  used,  and  since  most  ordinary  particles  found  in  ores  will 
be  found  to  be  negatively  charged,  they  migrate  toward  the  anode. 
As  mentioned  earlier  in  this  paper,  we  are  able  to  control  these  charges 
by  the  use  of  the  proper  electrolytes  added  to  the  suspensions  and 
thereby  control  the  direction  in  which  they  migrate  and  the  speed  at 
which  they  migrate.  The  water  migrates  in  the  opposite  direction,  and 


«No.  670,351,  720,186,  894,070,  993,888,  1,027,004,  1,029,579,  1,053,303,  1,098,- 
176,  1,120,551,  1.121,408,  1,121,409,  1,133,967,  and  1,156,715;  British  Pat.  No. 
24,670  of  1904,  3364  of  1911,  2379  of  1911,  11,626  of  1911,  27,930  of  1911,  27,931 
of  1911,  28,185  of  1911,  23,545  of  1912,  24,666  of  1912,  14,369  of  1912,  and  11,823 
of  1914;  German  Pat.  No.  239,649,  249,983,  251,098,  252,370,  253,429,  253,931, 
265,628,  266,825,  and  272,383. 


354  FLOTATION 

if  the  particles  are  congealed  into  a  gel  or  into  a  porous  diaphragm, 
the  water  can  still  migrate  when  the  electric  current  is  passed.  This 
travel  of  the  water  is  known  as  electro-endosmosis,  or  electro-osmosis. 
It  was  first  noticed  in  electrolytic  cells -containing  porous  diaphragms, 
such  as  have  been  used  in  the  electrolysis  of  brine  solutions  for  the 
formation  of  chloride  and  sodium  hydrate.  The  motion  of  the  particle 
through  the  liquid  is  known  as  electro-phoresis.  When  a  particle 
migrates  toward  the  anode,  the  phenomenon  has  been  called  cataphor- 
esis  and  when  it  migrates  toward  the  cathode,  the  phenomenon  is 
anaphoresis.  The  word  cataphoresis  is  often  used  in  place  of  electro- 
phoresis  for  the  reason  that  the  commonest  particles  met  usually  have  a 
negative  charge. 

One  special  application  of  this  migration  of  particles  and  water  is 
in  the  purification  of  clays.  This  process  has  been  described  by  Or- 
mondy7  in  the  purification  of  English  clays,  and  by  Bleininger8  for 
American  clays.  The  impure  clay  is  made  up  into  a  'slip'  of  the  con- 
sistence of  thick  cream,  by  the  use  of  water,  and  is  preferably  defloc- 
culated  by  the  use  of  a  little  sodium  hydrate.  The  coarse  particles,  as 
-well  as  some  of  the  iron  minerals  present,  separate  out  by  sedimenta- 
tion. The  suspension  is  run  into  a  metal  trough  into  which  dips  a 
revolving  horizontal  cylinder  made  of  lead  or  type-metal.  The  cylinder 
is  made  the  anode  and  the  trough  the  cathode  for  the  passage  of  an 
electric  current  under  110  to  220  volts.  Bleininger9  gives  a  photograph 
of  a  laboratory  machine  of  this  type,  and  Schwerin10  gives  a  sketch  of 
a  larger  machine. 

Under  the  influence  of  the  current  the  clay  is  deposited  on  the  type- 
metal  cylinder,  which  rotates  slowly,  and  the  deposited  blanket  of  pure 
clay  (this  deposit  is  about  \  in.  deep)  is  scraped  off  at  the  top  by  a 
scraper.  This  clay  contains  about  17%  moisture,  which  is  less  than 
that  remaining  after  filter-pressing  with  a  pressure  of  2  tons  per 
square  inch,  and  the  clay  is  whiter  and  more  plastic  than  the  impure 
original  clay.  The  velocity  of  migration  of  the  particles  is  about 
43xlOr<  cm. /sec. /volt/cm.,  which  is  about  the  same  rate  as  that  of  many 
ordinary  ions  in  solutions.  Hence  the  clay  slip  requires  stirring  to 
bring  the  particles  in  contact  with  the  cathode  in  large  enough  num- 
bers to  prevent  water  being  electrolyzed  by  the  current  instead  of  the 
particles  being  deposited.  The  cost  of  current  in  England  for  the 


7Trans.  Eng.  Ceramic  Soc.,  Vol.  XII,  pp.  36-64  (1912-13). 
sTrans.  Am.  Ceramic  Soc.,  Vol.  XV,  p.  335  (1913). 
sTechnologic  papers  of  the  Bureau  of  Standards,  No.  51 
loll.  S.  Pat.  No.  1,333,967. 


CONTROL    OP    ORE-SLIME  355 

depositing  of  a  ton  of  clay  is  from  10  to  64c.,  and  a  plant  capable  of 
producing  40  tons  per  week  of  finished  product  will  cost  $25,000. 

Bleininger  is  of  the  opinion  that  the  greatest  use  of  this  machine 
will  be  as  a  substitute  for  the  filter-press.  Recent  experiments  seem 
to  bear  out  that  opinion.  Most  of  the  impurities  of  the  clays  are  re- 
moved during  the  period  of  sedimentation  preceding  the  electro- 
phoresis,  and  the  only  function  of  the  electrical  operation  is  to  remove 
the  clay-particles  from  the  suspension  in  a  fairly  dry  state.  When 
very  colloidal  ore-slimes  resist  all  attempts  at  filtration,  this  method 
of  collecting  may  prove  useful.  Experiments  with  ordinary  free- 
settling  slime  by  this  method  have  been  carried  on  in  my  laboratory 
and  have  shown  that  most  of  the  particles  are  too  large  to  be  handled 
effectively  by  the  method.  With  a  clayey  ore  capable  of  a  high  degree 
of  dispersion,  better  results  can  be  obtained,  although  they  are  still  far 
from  what  can  be  done  with  the  true  clays. 

In  passing  it  might  be  well  to  call  attention  to  the  fact  that 
Schwerin's  patents  contain  a  wealth  of  information  on  the  properties 
of  various  suspended  particles  and  on  methods  of  controlling  them. 
He  finds,  for  instance,  that  a  particle  more  or  less  indifferent  toward 
the  electric  current  can  often  be  electrified  into  life  by  the  addition  of 
some  colloid  body,  such  as  colloidal  silicic  acid,  and  a  deflocculating 
agent,  like  sodium  hydrate.  The  colloidal  silicic  acid  is  adsorbed  on  the 
surfaces  of  the  indifferent  suspended  particles,  and  the  resulting  com- 
posite particles  are  more  active.  Sodium  silicate  will  hydrolize  into 
silicic  acid  and  sodium  hydrate ;  hence  it  is  at  once  a  combined  activat- 
ing and  deflocculating  agent.  In  another  place  he  mentions  the  fact 
that  with  a  well-deflocculated  suspension  the  consumption  of  electric 
energy  is  less  and  the  speed  of  the  particles  greater. 

The  importance  of  the  investigation  of  all  these  colloidal  phenomena 
in  their  bearing  on  the  control  of  ore-slimes  need  not  be  magnified. 
They  are  mentioned  in  the  hope  that  further  research  will  be  instigated 
by  parties  who  can  profit  by  the  results  of  such  investigation. 

Most  of  the  original  work  to  be  reported  in  this  paper  deals  with 
the  subject  of  slime-settling,  my  original  object  having  been  to  control 
the  rate  of  settling  of  ore-slimes  by  the  application  of  the  principles 
of  colloid  chemistry.  As  previously  mentioned,  it  has  been  possible  to 
make  almost  any  slime  settle  faster  or  slower,  and  some  success  has 
been  attained  in  differential  settling. 

The  use  of  lime  for  the  flocculation  of  low-settling  slimes  has  been 
common  practice  among  cyanide  operators,  and  many  a  cyanide  plant 
would  not  be  able  to  work  without  the  use  of  lime.  Slow-settling  slimes 


356  FLOTATION 

in  which  the  individual  particles  can  hardly  be  distinguished,  can 
often  be  caused  to  gather  into  large  floccules  by  the  addition  of  small 
percentages  of  caustic  lime.  These  large  nocks  settle  with  much  greater 
speed  than  do  the  small  individual  particles.  Nicolai11  gives  the  results 
of  recent  work  in  Germany  on  the  clarification  of  muddy  mill-water 
by  the  use  of  magnesium  chloride,  a  waste-product  from  the  potash 
works.  Magnesium  chloride  is  an  effective  coagulant. 

The  idea  of  deliberately  causing  a  slime  to  settle  more  slowly  does 
not  seem  to  have  been  applied  by  anyone.  There  are,  however,  conditions 
under  which  such  deflocculation  could  be  utilized,  aside  from  those 
already  mentioned.  For  instance,  the  work  reported  here  shows  that 
it  is  possible  to  deflocculate  the  so-called  true  slimes  so  that  the  coarser 
material  can  settle  out  of  the  suspension  separately.  This  would  be 
the  ideal  separation  of  non-leachable  material  from  leachable  sand, 
which  the  Dorr  and  similar  classifiers  approximate.  Under  these  con- 
ditions the  sand  that  settles  will  not  be  coated  with  entrained  slime. 
In  fact,  the  Dorr  classifier  could  be  used  to  make  the  improved  separa- 
tion. 

Another  application  of  deflocculation  could  be  made  in  the  transfer 
of  slime  through  launders  over  considerable  distances  on  level  ground. 
When  deflocculated,  the  slime  does  not  tend  to  settle  out  so  badly,  and 
on  arriving  at  its  destination  it  could  be  flocculated  and  deposited 
by  the  use  of  the  proper  agent.  Ditches  that  have  become  clogged  with 
clay  ought  to  be  opened  up  by  occasional  flushing  with  water  contain- 
ing a  deflocculating  agent,  while  the  settled  material  can  be  loosened 
by  drags.  The  use  of  lye  to  open  clogged  drain-pipes  is  a  familiar 
example.  Deflocculated  clay  slips  have  much  less  viscosity  than  or- 
dinary clay  slips,  and  a  piece  of  damp  clay  will  almost  liquefy  upon 
the  addition  of  small  amounts  of  the  proper  alkalies.  With  these  points 
in  view,  there  seemed  to  be  a  sufficient  encouragement  for  the  following 
series  of  systematic  investigations. 

Owing  to  the  fact  that  the  chief  interest  of  the  mill-man  lies  in  the 
rate  at  which  he  can  draw  off  clear  water  from  a  thickening-tank  and 
what  will  be  the  percentage  of  solids  in  the  thickened  pulp,  the  follow- 
ing method  was  used  in  the  study  of  the  rate  of  settling : 

A  series  of  200-c.c.  graduates  of  approximately  the  same  size  was 
obtained,  and  weighed  quantities  of  ore  were  introduced  into  the 
graduates,  which  first  were  partly  filled  with  water.  The  rise  of  the 
water-surface  on  the  introduction  of  the  ore  allowed  a  measure  of  the 
volume  of  the  ore,  and  knowing  its  weight  and  volume,  the  density  of 


und  Erz,  Vol.  Ill,  pp.  135  and  155  (1915). 


CONTROL    OF    ORE-SLIME  357 

the  dry  ore  could  be  calculated.  The  graduate  was  then  filled  to  the 
200-c.c.  mark.  By  placing  the  hand  over  the  mouth  of  the  graduate  and 
inverting  and  shaking  several  times,  it  was  possible  to  suspend  the  ore 
homogeneously  in  the  water  before  the  graduate  was  put  down  and 
settling  allowed  to  begin.  The  rate  of  subsidence  of  the  surface  of  the 
settling  slime  was  then  noted.  As  the  particles  in  the  suspension  have 
zero  velocity  at  the  beginning,  the  rate  of  subsidence  of  the  slime- 
surface  increases  to  a  maximum  and  then  diminishes  as  the  density  of 
the  thickened  pulp  increases,  causing  the  particles  to  get  more  and 
more  in  one  another's  way.  In  Free's  series  of  papers  we  find 
that  he  observed  the  position  of  the  surface  of  the  consolidated  slime 
in  the  bottom  of  the  graduate,  instead  of  the  surface  of  the  sinking 
column  of  thickening  slime.  Either  method  gives  us  an  idea  of  the 
average  rate  of  settling  of  the  slime-particles. 

With  dilute  suspensions,  the  larger  particles  tend  to  drop  out  first 
and  the  smaller  particles  gradually  thin  out  of  the  upper  layers  of  the 
water  so  that  no  definite  upper  surface  of  the  thickening  slime  is 
formed.  However,  with  most  ore-slimes  this  is  only  a  tendency,  as  the 
smaller  particles  sink  with  a  measurable  velocity  and  the  surface  of  the 
thickening  slime  will  be  indistinct  and  hazy,  owing  to  these  slowly- 
settling  particles  tending  to  cloud  the  clarified  water  above.  Later 
this  hazy  surface  of  the  thickened  slime,  at  a  perfectly  definite  position 
and  at  a  perfectly  definite  time,  will  suddenly  change  to  a  sharp  line 
of  separation  between  the  settling  slime  and  the  clarified  water.  Shortly 
after  this  the  rate  of  settling  of  this  surface  will  fall  off  greatly.  With^ 
slimes  containing  more  and  more  solids  at  the  beginning  of  settling, 
the  position  at  which  this  line  appears  is  higher  and  higher  up  in  the 
tube,  although  it  takes  a  measurable  length  of  time  for  any  previously 
agitated  slime  to  consolidate  to  a  condition  such  that  a  definite  line  of 
demarcation  can  form.  With  thick  slimes  and  when  well  flocculated, 
the  line  appears  in  a  few  seconds  and  practically  at  the  surface  of  the 
water. 

This  difference  in  behavior  between  dilute  and  concentrated  sus- 
pensions is  undoubtedly  due  to  the  fact  that  in  the  dilute  suspensions 
the  particles  fall  individually,  while  in  the  concentrated  suspensions 
they  seem  to  settle  collectively.  The  particles,  when  falling  individ- 
ually, exhibit  the  greatest  speed  of  settling.  In  Free's  papers  I  find 
much  the  same  observation.  He  has  termed  the  two  types  of  settling 
'subsidence'  and  'consolidation.'  In  order  to  avoid  confusion  of 
nomenclature,  I  have  adopted  his  terms  in  the  following  discussion. 
Nearly  all  the  dilute  suspensions  of  slimes  that  I  have  studied  begin  to 


358 


FLOTATION 


settle  by  subsidence  until  at  a  definite  concentration  of  solids  the  line 
appears  and  consolidation  settling  begins.  With  most  commercial 
.pulp-densities  subsidence-settling  takes  place  only  to  a  limited  extent 
unless  the  slime  is  deflocculated.  It  is  rare  that  the  mill-man  deals 
with  as  slow-settling  a  slime  as  Free's  kaolin  suspensions. 

In  addition  to  the  two  types  of  settling  already  mentioned,  I  have 
observed  a  third,  for  which  I  propose  the  name  'compacting.'  With 
most  freely-settling  ore-slimes,  this  type  of  settling  sets  in  at  about 
40%  solids,  illustrated  in  Fig.  1  and  2.  During  this  phase  of  settling, 


20  50  40  50  60 

Time      in      Minuses 

FIG.  1 


70         80 


the  thick  material  in  the  bottom  of  the  graduates  seems  to  be  slowly 
re-arranging  itself  into  closer  packing.  The  rate  of  settling  is  always 
considerably  slower  than  during  consolidation.  When  long  settling 
tubes  are  used,  the  material  that  has  settled  onto  the  bottom  first  is  well 
compacted  by  the  time  the  column  of  slime  above  it  has  reached  the 
consolidation  stage,  and  hence  consolidation  shades  imperceptibly  into 
compacting.  Only  short  tubes  showed  this  particular  phenomenon, 
and  as  Free's  work  was  with  long  tubes,  his  results  do  not  show 
the  compacting  stage.  In  my  own  work  the  compacting  was  very  evi- 
dent in  the  200-c.c.  graduates,  which  were  about  10  in.  deep.  It  was 
not  observed  in  a  tube  giving  a  column  of  36  inches. 

Roughly  speaking,  most  ordinary  dilute  slimes  will  settle  by  sub- 
sidence until  the  thickened  material  reaches  about  10-20%  solid,  at 
which  point  the  surface  of  the  settling  material  suddenly  becomes 
clear-cut  and  the  settling  enters  the  consolidation  phase,  which  it 
pursues  until  the  pulp  contains  an  average  of  about  40%  solid,  where 


CONTROL    OF    ORE-SLIME 


359 


it  enters  the  compacting  phase.  Some  decrease  in  velocity  is  noticed 
on  passing  from  the  subsidence  to  the  consolidation  phase,  but  a  great 
decrease  in  velocity  often  takes  place  on  passing  into  the  compacting 
phase.  As  will  be  seen  later,  the  effect  of  the  addition  of  electrolytes 
and  of  colloids  is  to  shift  the  critical,  or  transition,  points  (where  the 
settling  changes  from  one  phase  to  another). 


ing,  Miilitne+ers  per  Minute 
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Velocity  of  Sethi 

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10                    20                   30                   40 

Percentage  Solids  in  Thickened  Pulp 
FIG.  2 

The  only  feasible  explanation  of  the  difference  between  subsidence 
and  consolidation  would  appear  to  be  the  following:  In  dilute  sus- 
pensions the  larger  particles  of  the  slime  would  tend  to  settle  relatively 
faster  than  the  others,  and  in  dilute  suspensions  they  can  go  down 
without  entraining  smaller  particles;  so  the  latter  are  left  behind  to 
settle  more  slowly.  Hence  the  water  above  the  subsiding  slime  is 
always  somewhat  cloudy.  With  more  concentrated  suspensions  it  is 
possible  to  reach  a  consistence  in  which  the  distance  between  the  larger 
particles  is  so  small  that  the  particles  of  smaller  size  are  trapped  and 
carried  down.  This  suspension  of  the  larger  particles  might  be  re- 
garded as  a  filter  for  the  suspension  of  the  smaller  particles. 


360  FLOTATION 

THE  FLOTATION  OF  OXIDIZED  ORES 

BY  GLENN  L.  ALLEN  AND  OLIVER  C.  RALSTON 
(Written  especially  for  this  volume) 

INTRODUCTION.  ^Concentration  of  sulphide  ores  by  flotation  has 
met  with  such  success  that  attempts  have  recently  been  made  to  apply 
the  process  to  the  flotation  of  ores  other  than  natural  sulphides.  Most 
of  the  experimental  work  in  our  laboratory  at  the  Utah  station  has 
been  done  on  the  oxidized  ores  of  lead.  Only  minor  attention  has 
been  given  to  the  oxidized  ores  of  zinc  and  of  copper,  for  the  following 
reasons:  little  success  has  been  had  with  the  zinc  ores;  many  others 
are  engaged  in  testing  copper  ores,  so  that  there  was  no  pressing  ne- 
cessity for  experimentation  with  copper  ores  by  the  Bureau,  although 
an  attempt  has  been  made  to  co-ordinate  the  work  of  those  who  are 
willing  to  join  in  solving  the  problem.  Flotation  of  oxidized  minerals 
depends  upon  a  preliminary  'sulphidizing'  by  any  method  that  will 
convert  at  least  the  surface  of  the  mineral  particles  to  a  sulphide  of 
the  metal.  This  step  is  followed  by  flotation  of  the  artificial  sulphide. 

PATENTS.  The  first  method  for  the  flotation  of  oxidized  ores  to  ap- 
pear in  patent  literature  was  that  of  F.  B.  Dick.  It  is  contained  in 
British  patent  16,667  of  1908.  This  method  calls  for  the  reduction  of 
the  oxide  to  metal  in  a  furnace  with  a  reducing  atmosphere,  followed 
by  the  flotation  of  the  ' prills'  of  metal  formed.  As  lead  and  copper 
are  the  only  two  common  metals  easily  reduced  to  the  metallic  form, 
it  is  probable  that  Dick  had  no  others  in  mind.  He  mentions  the 
oxidized  ores  of  copper  in  silicious  gangue  from  the  Benguella  and 
Katanga  districts  of  Central  Africa  as  being  amenable  to  this  kind 
of  treatment.  From  the  coarse  grinding  recommended  by  him 
(20-mesh)  it  is  probable  that  he  had  in  mind  either  the  film  or  the 
bulk-oil  types  of  flotation. 

In  British  patent  No.  8650  of  1910,  Sulman  &  Picard,  of  Minerals 
Separation,  Ltd.,  have  patented  a  like  idea,  evidently  with  froth-flota- 


*This  review  of  the  subject  is  based  mainly  on  a  paper,  by  the  same 
writers,  issued  by  the  U.  S.  Bureau  of  Mines  in  July  1916.  There  has  been 
added  a  discussion  of  the  patent  literature  dealing  with  the  subject.  The  text 
also  is  altered  somewhat  to  include  more  recent  information.  Most  of  the 
portion  concerning  flotation  of  lead-carbonate  ores  has  been  revised  by  Mr. 
Allen,  who  has  continued  his  work  while  in  the  employ  of  the  Shattuck- 
Arizona  Copper  Co.,  in  whose  Bisbee  mine  a  large  tonnage  of  lead-carbonate 
ore  has  been  disclosed  while  mining  copper  ore.  N.  C.  Christensen  and  R.  W. 
Johnson  have  assisted  in  collecting  some  of  the  evidence  on  which  the  con- 
clusions of  this  paper  are  based. 


FLOTATION    OF    OXIDIZED    ORES  361 

tion  in  mind.  They  claim  the  application  to  metals  in  ' '  easily  reducible 
oxides. ' '  Such  metals  as  lead  and  copper  are  mentioned.  One  specific 
application  is  the  treatment  of  mixed  zinc  and  lead  oxidized  ores.  The 
lead  can  be  reduced  easily  in  a  reducing  atmosphere  at  600°  C.  while 
the' oxidized  zinc  compounds  are  unaffected  at  this  temperature.  After 
cooling  the  reduced  product  out  of  contact  with  the  atmosphere  the 
lead  could  be  floated  away  from  the  zinc.  We  have  not  tested  this 
process  thoroughly  but  we  are  inclined  to  believe  that  oxidized  forms 
of  copper  are  more  likely  to  be  reduced  to  an  easily  separable  form 
than  oxidized  forms  of  lead.  However,  in  the  examination  of  the  re- 
duced product  of  copper  prepared  by  others  for  proposed  gravity- 
separation  small  shots  of  metallic  copper  could  be  seen  attached  to  the 
gangue.  After  the  reduction  it  would  be  necessary  to  grind  the 
product  to  liberate  the  'prills'  and  'leaves'  of  metal  from  the  gangue. 

Treatment  of  complex  sulphides  by  this  process  assumes  that  the 
ore  is  first  roasted  to  oxides  before  reduction.  In  case  part  of  the  me- 
tallic sulphides  is  roasted  only  to  sulphates  these  would  tend  to  be  re- 
duced to  sulphides  again  during  the  reduction  period.  In  the  case  of 
mixed  lead  and  zinc  sulphide  ores  it  would  be  all  right  to  allow  the 
lead  to  roast  to  sulphate  (which  is  easily  accomplished),  but  any  sul- 
phate or  basic  sulphate  of  zinc  would  be  undersirable,  because  the  sul- 
phide of  zinc  formed  would  tend  to  float. 

The  first  American  patent  covering  sulphidizing  and  flotation  is 
that  of  Alfred  Schwarz  (U.  S.  807,501  of  December  19,  1905).  It 
was  taken  out  coincidently  with  other  patents  covering  methods  of 
bulk-oil  flotation,  for  froth-flotation  was  only  then  being  started.  He 
claims  the  use  of  any  'soluble  sulphide'  and  states  that  he  generally 
uses  an  excess  of  sulphur  over  that  theoretically  necessary  to  convert 
the  oxide,  carbonate,  or  chloride  of  the  metal  in  question  completely 
to  the  sulphide.  A  poly-sulphide  of  sodium  made  by  boiling  sulphur 
and  caustic  soda  is  mentioned. 

The  next  mention  of  sulphidizing  and  flotation  of  oxidized  minerals 
was  in  British  patent  26,019  of  1909  by  Sulman  &  Picard.  This  patent 
shows  familiarity  with  the  sulphidizing  and  flotation  of  ores.  While 
oxidized  copper  ores  are  given  a  prominent  place,  the  sulphidizing  of 
oxidized  ores  of  lead  is  also  mentioned.  Hydrogen  sulphide,  as  well  as 
other  soluble  sulphides,  is  said  to  be  suitable,  and  it  is  here  that  the 
use  of  sulphur  vapor  is  first  mentioned  in  patent  literature.  One  vari- 
ation of  this  method  is  to  heat  the  powdered  ore  with  pyrite  in  a  neu- 
tral or  reducing  atmosphere.  Such  treatment  distills  the  feeble  atom 
of  sulphur  from  the  pyrite,  so  that  the  sulphur  combines  with  the  oxi- 
dized lead. 


362  FLOTATION 

Joseph  T.  Terry,  in  U.  S.  1,094,760  of  April  28,  1914,  describes  the 
use  of  hydrogen-sulphide  gas  in  a  flowing  pulp  of  an  oxidized  ore  of 
copper  (other  metals  also  are  claimed)  with  a  suitable  apparatus  for 
the  recovery  of  any  excess  gas  after  sulphidizing  the  pulp.  The  use  of 
sodium  sulphate  is  also  described  and  the  addition  of  copper  sulphate 
to  help  in  the  formation  of  nuclei  of  copper  sulphide  around  which 
the  formation  of  sulphide  granules  and  coagulations  can  take  place. 

H.  B.  Hoveland  and  G.  B.  Frankforter  entered  the  sulphidizing 
field  with  U.  S.  patent  1,098,668  of  June  2,  1914.  This  claims  the  ap- 
plication of  hydrogen-sulphide  gas  to  dry  ore  for  the  sulphidizing  of 
oxidized  minerals  previous  to  flotation.  It  claims  advantage  in  the 
greater  rapidity  of  the  sulphidizing  reactions,  10  to  20  minutes  in  an 
atmosphere  of  hydrogen-sulphide  gas  being  said  to  be  sufficient.  From 
the  known  great  velocity  of  diffusion  of  gas  molecules  as  compared  to 
the  velocity  of  the  diffusion  of  the  same  molecules  when  in  aqueous  so- 
lution, such  a  claim  seems  justifiable.  Our  own  experience  on  lead  ores 
does  not  verify  this  statement,  as  will  be  seen  later.  However,  Hove- 
land and  Frankforter  mention  the  carbonate  ores  of  copper  in  illus- 
trating their  process  while  our  work  has  been  confined  largely  to  the 
carbonates  of  lead.  A  surprising  claim  is  made  for  the  sulphidizing  of 
an  oxidized  capping  in  place.  The  patentees  state  that  the  gas  mole- 
cules finally  penetrate  to  the  centres  of  the  masses  of  ore,  sulphidizing 
the  oxidized  minerals  of  copper  and  disintegrating  the  rock  so  that  it 
can  be  more  easily  mined. 

Raymond  F.  Bacon,  in  U.  S.  1,140,865,  of  May  25,  1915,  discloses 
the  use  of  hydrogen  sulphide  and  sulphur  di-oxide  in  a  pulp  to  effect 
flotation  by  means  of  the  colloidal  sulphur  resulting  from  the  reac- 
tion of  these  two  chemicals.  The  colloidal  sulphur  is  said  to  serve  as 
a  substitute  for  flotation-oil.  By  introducing  hydrogen  sulphide  first 
the  oxidized  minerals  can  receive  a  sulphide  coating  before  the  excess 
of  hydrogen  sulphide  is  neutralized  by  the  introduction  of  sulphur  di- 
oxide. This  feature  is  embodied  in  another  of  Bacon's  patents,  No. 
1,140,866  of  May  25,  1915,  and  is  described  in  connection  with  some 
tests  of  an  oxidized  copper  ore.  "One  ton  of  oxidized  copper  ore  con- 
taining 2%  of  copper,  and  crushed  to  pass  a  60-mesh  screen,  is  placed 
in  a  Pachuca  tank  with  three  tons  of  water.  The  air  is  turned  on  and 
the  water  agitated  for  a  few  minutes,  just  enough  to  obtain  a  good  mix- 
ture of  the  ore  and  water.  Immediately  after  the  violent  agitation  has 
ceased  and  while  considerable  of  the  ore  is  still  in  suspension  hydro- 
gen sulphide  is  forced  into  the  body  of  ore  and  water  through  suitable 
inlet-pipes  in  the  bottom  of  the  Pachuca  tank.  With  the  ore  used  in 


FLOTATION    OF    OXIDIZED    ORES  363 

this  experiment  60  cu.  ft.  of  hydrogen  sulphide  was  admitted.  This 
amount  of  hydrogen  sulphide  is  not  sufficient  to  convert  all  the  oxi- 
dized copper  present  into  the  sulphide,  but  for  purposes  of  flotation 
this  is  not  necessary.  It  is  only  necessary  to  form  a  surface-film  of 
copper  sulphide  surrounding  each  oxidized  particle.  The  mixture  of 
ore  and  water  is  allowed  to  stand  a  few  minutes  with  the  hydrogen  sul- 
phide, then  a  slight  excess  of  sulphur  di-oxide  is  run  in  through  the 
inlet  in  the  bottom  of  the  tank.  The  sulphur  di-oxide  gas  used  for 
this  purpose  may  be  the  pure  gas  or  dilute  impure  gases  such  as 
smelter  fumes.  In  case  the  latter  are  used  they  may  be  introduced  in 
place  of  air  to  effect  the  agitation  of  the  mixture.  A  short  time  after 
the  introduction  of  the  sulphur  di-oxide  the  mixture  of  ore,  water,  etc., 
is  tested  with  lead-acetate  paper  and  when  the  hydrogen  sulphide  has 
disappeared  the  mixture  is  allowed  to  flow  into  a  flotation-tank,  where 
the  sulphide-coated  copper  oxide,  carbonate,  and  silicate  particles  are 
floated  off  and  thus  separated  from  the  gangue.  With  the  particular 
ore  cited,  a  recovery  of  83%  of  the  copper  was  thus  effected,  the  con- 
centrate containing  21%  copper." 

Our  own  tests  show  that  it  is  very  difficult  to  obtain  flotation  after 
the  pulp  has  been  treated  with  sulphur  di-oxide.  Sulphur  di-oxide  and 
the  sulphites  are  known  as  inhibitors  of  flotation,  and  yet  Bacon 
makes  the  claim  that  better  flotation  is  obtained  in  the  presence  of  a 
slight  acidity  due  to  sulphur  di-oxide.  Bacon 's  process  is  not  as  sim- 
ple as  it  sounds. 

In  U.  S.  patent  1,197,589  of  September  12,  1916,  he  has  still  fur- 
ther broadened  his  claims,  and  states  that  this  patent  is  an  improve- 
ment over  his  former  method.  This  patent  is  well  written.  He  has 
reversed  the  order  of  application  of  the  two  gases.  Sulphur  di-oxide 
is  applied  first  in  order  to  convert  all  of  the  copper  to  sulphite  and 
the  subsequent  treatment  with  hydrogen  sulphide  precipitates  the  cop- 
per as  sulphide.  He  states  that  it  is  not  necessary  to  obtain  complete 
solution  of  all  the  copper  before  precipitation  although  it  may  be  best 
with  some  ores.  Colloidal  sulphur,  from  the  reaction  of  sulphur  di- 
oxide on  hydrogen  sulphide,  is  also  produced  and  the  claim  is  made 
that  this  acts  as  a  substitute  for  flotation-oil  in  whole  or-  in  part,  re- 
sulting in  better  flotation.  In  case  an  ore  contains  lead,  copper,  and 
zinc  the  copper  and  zinc  go  into  solution.  The  hydrogen  sulphide  pre- 
cipitates only  the  copper  from  solution  and  it  is  then  floated  out.  A 
subsequent  precipitation  of  the  zinc  with  an  alkaline  sulphide  renders 
it  amenable  to  subsequent  flotation.  We  regard  this  as  a  most  extrav- 
agant claim. 


364  FLOTATION 

A  few  months  later  Hoveland  took  out  another  patent  for  the  sul- 
phidizing of  minerals,  U.  S.  1,159,942  of  November  9,  1915.  It  is 
claimed  that  in  the  application  of  calcium  sulphide  for  the  sulphidiz- 
ing of  minerals  the  action  is  greatly  accelerated  by  the  presence  in  the 
solution  of  some  ferric  sulphate.  Sulphuric  acid,  or  sulphur  di-oxide 
and  oxygen,  is  first  applied  to  the  ore-slime  to  form  copper  sulphate. 
On  addition  of  calcium  poly-sulphide  and  ferric  sulphate  to  the  pulp 
copper  sulphide  is  formed  and  can  be  removed  by  flotation.  The  func- 
tion of  ferric  sulphate  is  to  oxidize  any  excess  sulphurous  acid.  We 
fail  to  see  the  advisability  of  getting  copper  into  solution  and  then  re- 
precipitating  it  as  sulphide,  except  that  flotation  serves  as  a  substitute 
for  filtration.  Since  lead  carbonate  does  not  go  into  solution,  the  same 
advantages  are  not  obtained  and  this  method  offers  no  apparent 
advantage  when  applied  to  lead  ores. 

Later  Hoveland  obtained  two  more  patents;  these  covered  the  use 
of  apparatus  for  carrying  his  invention  into  effect.  These  patents  were 
1,164,188  and  1,164,189  of  December  14,  1915.  The  idea  that  seems  up- 
permost in  his  mind  is  that  of  sulphating  the  ore  by  treatment  with 
sulphur  di-oxide  and  oxygen  under  pressure  in  a  specially  constructed 
agitating-apparatus,  arranged  for  continuous  operation.  He  claims 
that;  the  sulphating  under  pressure  of  minerals  like  copper  carbonate 
in  such  an  apparatus  is  much  quicker  and  more  complete  than  at  ordi- 
nary atmospheric  pressure.  Here  he  explains  that  in  order  to  sulphi- 
dize  the  sulphated  material  well  with  calcium  poly-sulphide  the  excess 
of  sulphur  di-oxide  can  be  oxidized  by  the  presence  of  ferric  sulphate. 
In  fact,  we  believe  that  Hoveland  could  not  conduct  flotation  well  if 
sulphur  di-oxide  or  sulphites  were  present  in  his  pulp  in  any  consider- 
able quantity.  His  apparatus  is  also  adapted  for  flotation  in  a  closed 
vessel,  so  that  the  same  air  could  be  used  over  and  over  again  for  flo- 
tation, and  if  necessary  some  other  gas  than  air  could  be  employed,  in 
order  to  prevent  re-oxidation  of  the  precipitated  copper  sulphide. 

Bacon  was  the  next  patentee  (U.  S.  patent  1,180,816  of  April  25, 
1916).  His  patent  covered  the  use  of  hydrogen  sulphide  under  pres- 
sure during  sulphidizing.  One  of  the  most  recent  ideas  is  contained 
in  his  patent  No.  1,197,590  of  September  12,  1916.  This  deals  with 
both  oxidized  ores  and  those  that  can  be  wholly  or  partly  roasted.  The 
application  to  the  mixed  sulphide  ores  is  discussed  in  this  volume  un- 
der " Differential  Flotation."  Occasionally  an  oxidized  ore  contain- 
ing lead  and  zinc  carbonates  is  so  intimately  intergrovvn  that  on  apply- 
ing a  sulphidizing  agent  it  is  possible  to  film  the  lead  carbonate  with 
lead  sulphide,  but  so  much  zinc  is  entrained  with  the  lead  that  flotation 


FLOTATION    OF    OXIDIZED    ORES  365 

fails  to  separate  them.  As  will  be  seen  later,  zinc  carbonate  does  not 
appear  to  sulphidize  under  these  conditions  and  occasionally  the  lead 
carbonate  can  be  separated  from  a  free  ore.  But  when  it  is  not  freed 
by  crushing,  Bacon  proposes  to  treat  the  ore  with  an  acid,  such  as  sul- 
phuric, converting  the  lead  to  the  insoluble  sulphate  and  the  zinc  to  a 
solution  of  zinc  sulphate.  On  treating  the  pulp  with  hydrogen  sul- 
phide the  lead  is  converted  to  sulphide  and  any  silver  or  copper  are 
likewise  converted  to  sulphides,  while  the  solution  of  zinc  sulphate,  be- 
ing acid,  is  unaffected.  Flotation  is  then  supposed  to  remove  the  lead, 
silver,  and  copper.  After  this  has  been  accomplished,  the  acid  in  the 
pulp  is  neutralized  and  the  zinc  sulphate  converted  to  sulphide  by  ad- 
dition of  an  alkaline  sulphide.  The  zinc  sulphide  is  then  likewise  re- 
moved by  flotation.  By  these  methods  metals  like  copper,  lead,  silver, 
mercury,  cadmium,  and  bismuth  can  be  separated  from  metals  like 
iron,  zinc,  and  nickel  in  oxidized  ores.  The  flotation  is  merely  a  substi- 
tute for  filtration. 

As  mentioned  elsewhere,  the  chemistry  involved  in  this  patent  is 
good,  being  that  underlying  qualitative  analysis,  but  owing  to  the 
practical  difficulty  of  obtaining  satisfactory  flotation  in  the  presence  of 
such  soluble  compounds  as  iron  sulphate  and  copper  sulphate  we  doubt 
whether  this  process,  as  patented  by  Bacon,  can  be  made  to  work.  If 
the  patent  is  valid,  it  is  probably  broad  enough  in  its  claims  to  cover 
many  truly  meritorious  ideas  that  may  be  developed  and  that  will  not 
be  subject  to  the  same  difficulties. 

LEAD  CARBONATE.  The  necessity  of  a  process  for  the  recovery  of 
lead  from  its  low-grade  carbonate  ores  has  never  been  emphasized,  yet 
it  is  a  common  thing  to  find  old  mill-dumps  containing  from  5  to  10% 
of  lead  as  carbonate  in  a  finely  divided  form  incapable  of  satisfactory 
recovery  by  gravity  methods  and  too  'dry'  to  smelt.  The  tendency 
of  lead  carbonate  is  to  form  flakes ;  that  is  why  the  artificially  manu- 
factured basic  lead-carbonate,  used  as  a  paint  under  the  name  of 
'white  lead,'  is  efficient  in  covering  a  surface. 

As  the  flotation  process  is  applied  successfully  to  finely  divided 
material,  the  extension  of  the  process  to  slime  containing  lead  carbon- 
ate is  immediately  suggested.  So  far  the  most  promising  method  is  a 
preliminary  treatment  by  'sulphidizing,'  whereby  the  particles  of  lead 
carbonate  are  first  converted,  superficially  at  least,  into  the  sulphide  of 
lead,  which  is  amenable  to  ordinary  flotation. 

Several  ways  of  doing  this  have  been  proposed : 

1.  Sulphidizing  by  means  of  hydrogen  sulphide  gas  applied  to 
either  the  dry  crushed  ore  or  to  the  wet  pulp. 


366 


FLOTATION 


2.  Sulphidizing  by  means  of  a  solution  of  sulphide  of  sodium  or 
other  sulphur-compounds  of  sodium. 

3.  Sulphidizing  by  means  of  a  solution  of  calcium  poly-sulphide 
or  other  sulphur  compounds  of  calcium. 

4.  Sulphidizing  by  means  of  sulphur  vapor  applied  to  dry  crushed 
ore. 

5.  Sulphidizing   by   means  of   a   flotation-oil   containing  loosely 
combined  sulphur  and  capable  of  giving  up  the  sulphur  to  the  oxidized 
ore. 

6.  Sulphidizing  by  the  use  of  a  solution  of  colloidal  sulphur. 

Not  all  of  these  ideas  are  new ;  in  fact,  patent  claims  have  been 
made  that  are  probably  broad  enough  to  cover  them  all.  However,  ex- 
act data  as  to  the  effectiveness  of  the  various  methods  of  sulphidizing 
oxidized  ores  are  lacking. 

HYDROGEN  SULPHIDE  is  the  sulphide  most  naturally  suggested  as 
a  reagent  for  the  sulphidizing  of  ores.  This  was  the  first  reagent  tested 
by  us,  because  Hoveland's  patent  for  dry  sulphidizing  looked  so  tempt- 
ing. Some  of  the  best  results  with  dry  hydrogen  sulphide  are  given  in 
Table  I.  The  ore  tested  came  from  the  May  Day  mine  in  the  Tintic 


TaWe  1 

Su/pftidizing   with   dry   hydrogen   sc//pfr/de. 
Ore  from  May  Day  mine.  Utet>.        4.2%  /eod,  236  oz.  si/ver,  4.6%  /ran.  84%  inso/t/6/e. 
SOO  ym.  perfesf,   Janney  machine.     Of/,0-9  Ik.  per  ton.  (SunnySouM  p/ne-oiJJV2-S) 

No 

Sulph/d/zed 
Minutes 

HtSO* 

added  da  r  /riff 
f/ofation 

Weight 
Gm. 

frofh.  Analysis,  and   Recovery. 

Lead 

Silver 

/ron 

/nso/u6/e 

Assay  % 

Recovery  % 

\Assqyoi 

Recovery  % 

Assay  % 

Recovery  % 

SSSOJT'O 

Recovery  % 

/ 

/£ 

none 

3/3 

/3-3 

20.  /      _ 

//  7 

/S  3 

6O-O 

45 

2 

JO 

• 

^^  s 

96 

/O-l 

171 

/6-7 

S9.t 

32 

3 

60 

. 

40  S 

/3.7 

26.4 

S-74 

19-7 

/04 

/93 

606 

S  8 

4 

tao 

. 

S40 

8.7 

£2-3 

j.es 

242 

169 

397 

6O7 

7-8 

J 

460 

330 

S.S 

42.0 

424 

334 

147 

39-S 

366 

13  0 

6 

/s 

9S7fa  perfon 

23.  s 

229 

2-S-6 

/6-OO 

3/9 

ao-i 

20-  S 

302 

1-7 

7 

30 

• 

36.6 

2/-6 

37-  S 

I7S 

27-9 

332 

29 

A 

6O 

. 

39-S 

2/-3 

4O/ 

/3-SO 

4S2 

16  t 

Z.7-7 

3SO 

33 

5 

120 

• 

&.0 

2S.3 

6^  7 

11.70 

S/6 

//  J 

2SS 

386 

48 

A? 

460 

» 

6&.0 

2+6 

73.7 

9-60 

«H 

/04 

30-7 

374 

6-0 

district  of  Utah.  Practically  all  of  the  tests  were  performed  in  a  Jan- 
ney  machine.  At  first  we  thought  that  the  low  extraction  of  lead  fol- 
lowing a  short  time  of  sulphidizing  of  this  ore  in  the  dry  state  was  due 
to  the  rubbing  off  of  the  sulphide  film,  so  the  more  gentle  treatment 
possible  in  a  Callow  cell  was  tried.  Practically  identical  results  were 
obtained.  It  was  found  that  with  longer  treatment  with  hydrogen 
sulphide  the  extractions  increased  on  both  silver  and  lead.  Hence  the 
trouble  with  the  early  tests  must  have  been  due  to  insufficient  time  of 
gas  treatment.  It  was  surprising  to  see  the  way  in  which  the  gas  would 
react  with  the  ore.  When  placed  in  a  bpttle  on  a  rolling  agitator  the 


FLOTATION  OF  OXIDIZED  ORES  367 

ore  would  be  showered  through  the  atmosphere  of  hydrogen  sulphide 
like  the  material  in  the  old  Bruckner  furnace.  The  ore  would  begin  to 
blacken  almost  immediately  and  absorbed  the  hydrogen  sulphide  with 
such  avidity  that  a  considerable  amount  of  heat  was  generated.  Even 
after  eight  hours  treatment  with  the  gas  it  took  only  a  few  minutes  for 
the  ore  to  use  up  all  of  the  hydrogen  sulphide  remaining  in  the  bottle 
so  that  no  smell  of  hydrogen  sulphide  remained. 

The  second  group  of  experiments  in  Table  I  shows  plainly  that  the 
use  of  acid  in  the  flotation  of  the  sulphidized  pulp  is  absolutely  essen- 
tial both  for  getting  higher  recovery  of  the  lead  and  silver  from  the 
suphidized  ore  and  for  giving  a  suitable  grade  of  concentrate.  It  was 
found  that  this  ore  used  less  acid  than  many  of  the  other  ores  treated 
and  that  most  of  them  called  for  amounts  of  acid  nearer  to  300  Ib.  per 
ton  of  dry  ore  before  a  clean  concentrate  and  a  higher  recovery  could 
be  obtained.  Such  quantities  of  chemicals  are,  of  course,  prohibitive 
unless  they  can  be  obtained  very  cheaply. 

A  noticeable  concentration  of  iron  appears  in  the  flotation  concen- 
trate. The  iron  present  in  this  ore  was  largely  limonite.  It  was  de- 
termined by  visual  examination  that  the  iron  was  blackened  by  the 
hydrogen  sulphide,  thus  accounting  for  its  presence  in  the  concentrate. 

Application  of  the  hydrogen  sulphide  to  the  ground  ore  suspended 
in  water  gave  similar  recoveries  and  grades  of  concentrate,  the  only 
difference  being  that  the  amount  of  gas  used  was  much  smaller  and  it 
was  occasionally  possible  to  get  fair  work  done  in  a  neutral  solution — 
a  great  advantage.  On  the  whole,  we  think  it  improbable  that  hydro- 
gen sulphide  will  be  used  on  dry  ore  on  account  of  the  amount  of  chem- 
icals required.  Large  lumps  of  the  ore  when  exposed  to  the  hydrogen 
sulphide  in  a  bottle  reacted  vigorously,  and  on  breaking  them  open 
it  could  be  seen  that  the  gas  had  penetrated  deeply.  Hence,  we  feel 
justified  in  stating  that  when  sulphidizing -the  dry  ore  enough  gas 
must  be  applied  to  convert  all  of  the  lead  in  the  ore,  together  with  some 
of  the  oxidized  iron,  into  sulphides.  On  flotation,  the  application  of 
acid  will  break  up  the  iron  sulphide  with  evolution  of  hydrogen  sul- 
phide (this  was  observed),  while  lead  sulphide  is  fairly  stable  in  acidi- 
fied solutions.  As  the  hydrogen  sulphide  is  liberated  in  the  body  of 
the  ore  by  the  action  of  the  acid,  it  is  possible  that  the  gas  sulphidizes 
some  of  the  lead  and  silver  that  may  have  escaped  reaction  previously. 
Further,  after  the  iron  is  dissolved  by  the  acid  there  is  probably  more 
of  the  lead  sulphide  exposed  to  the  action  of  the  flotation-oil;  hence 
higher  recoveries  and  better  grades  of  concentrate  were  obtained  in  the 
tests  where  sulphuric  acid  was  added  during  flotation. 


368  FLOTATION 

All  of  the  above  shows  that  the  particles  are  not  merely  'filmed'  but 
are  entirely  converted  to  sulphide  of  lead.  In  the  wet  pulp  it  was  pos- 
sible to  use  much  less  than  the  theoretical  amounts  of  hydrogen  sul- 
phide and  to  get  better  recoveries,  so  that  only  a  'film'  on  the  lead 
carbonate  particles  could  have  been  transformed.  However,  sulphuric 
acid  was  still  necessary  in  order  to  get  clean  flotation  after  sulphidizing 
in  the  wet  pulp.  As  most  of  the  lead-carbonate  ores  contain  consider- 
able amounts  of  acid-soluble  material,  the  consumption  of  acid  was 
always  high.  This  caused  us  to  turn  to  the  alkaline  sulphides  as  a. 
method  of  sulphidizing. 

Much  of  the  old  literature  has  insisted  that  the  presence  of  hydro- 
gen sulphide  in  the  pulp  during  flotation  is  deleterious,  so  we  were 
much  surprised  that  some  of  our  best  work  was  obtained  when  a  sul- 
phidized  pulp  was  acidified,  giving  a  noticeable  odor  of  hydrogen  sul- 
phide. Therefore,  we  conclude  that  for  the  artificial  lead  sulphides, 
at  least,  the  former  belief  does  not  hold. 

Commercial  methods  of  making  hydrogen  sulphide  are  available  if 
a  demand  for  the  gas  should  be  created ;  in  fact,  it  is  being  used  on 
the  Magma  ore  at  Superior,  Arizona,  writh  marked  success.  The  sim- 
plest method  of  making  the  gas,  and  one  with  which  practically  every 
engineer  is  familiar  is  the  treatment  of  iron  matte  with  sulphuric  acid. 
Iron  matte  can  be  made  at  a  cost  of  from  $5  to  $10  per  ton  by  distilling 
the  feeble  atom  of  sulphur  from  pyrite  and  melting  the  residue.  Sul- 
phuric acid  is  available  at  from  $5  to  $20  per  ton  in  many  mining  dis- 
tricts. This  will  make  the  hydrogen  sulphide  cost  from  $30  to  $60  per 
ton.  Hydrogen  sulphide  can  also  be  made  from  calcium  sulphide  by 
treatment  with  carbonic  acid  gas — known  as  the  Chance  or  Claus- 
Chance  process : 

CaS+H20+C02=CaC03+H2S. 

Calcium  sulphide  can  be  prepared  by  the  reduction  of  gypsum.  An- 
other method  of  preparing  hydrogen  sulphide  consists  of  passing  sul- 
phur vapor,  mixed  with  excess  hydrogen  or  a  hydrocarbon  gas,  through 
a  heated  zone. 

The  greatest  objection  to  hydrogen  sulphide,  outside  of  the  cost 
of  chemicals,  is  its  bad  effect  on  workmen.  It  is  not  only  poisonous  but 
small  amounts  seriously  affect  the  nerves. 

SODIUM  SULPHIDE  was  chosen  as  a  more  promising  reagent  for  com- 
mercial sulphidizing.  The  results  contained  in  Table  II  will  show 
that  it  is  much  better  adapted  to  the  purpose. 

The  ore  from  the  Shattuck- Arizona  mine,  at  Bisbee,  has  given  the 
best  results.  As  can  be  seen  from  the  analysis  of  the  head  sample,  this 


FLOTATION    OF    OXIDIZED    ORES 


369 


ore  contains  lead,  silver,  and  gold.  It  is  possible  to  get  good  recoveries 
of  the  metals  in  a  high-grade  concentrate  by  the  application  of  only  a 
few  pounds  of  sodium  sulphide  per  ton  of  ore.  In  test  No.  4  the  ore 
(crushed  to  pass  80-mesh)  was  treated  for  2.66  hours  with  an  equal 
weight  of  1%  solution  of  sodium  sulphide  or  20  Ib.  Na2S  per  ton  of  ore. 
The  concentrate  collected  practically  all  of  the  lead  in  a  50.75%  lead 
product  containing  almost  all  of  the  silver  and  gold.  Theoretically,  an 
ore  containing  15.42%  lead  will  require  116  Ib.  sodium  sulphide  to  con- 
vert all  of  the  lead  into  the  sulphide  form.  As  this  ore  contains  no  sul- 
phur and  only  20  Ib.  of  sodium  sulphide  per  ton  was  used  on  it,  we 
have  good  proof  that  the  lead  carbonate  particles  are  being  converted 
only  superficially  into  the  sulphide  of  lead  by  the  solution  of  sodium 
sulphide.  In  other  words,  we  have  true  *  sulphide  filming.'  Since 
making  the  tests  in  Table  II  a  mill-run  has  given  equally  successful 


Table     II 

Sodium  Sulphide  <so/uf/ons    for  $u/ph/dtz/ngr. 
Ore  from   •Sftaffuc*-  Arizona  m/'ne.     SOO  cm  per  test     /S4e%/eod,  /Z88ozs//ver,  and  OOSoz.o-o/d  per  for) 

Mo. 

<Sod/um  Su/ph/de 

Hours 

f/ofof/o/j  o// 
tb.  per  fan 

Froth.  Ana/yses,  erno1  ffecover/es. 

Lead 

3//ver 

Gold 

/nso/i/6/e 

/ron 

Assay  % 

Recovery  % 

Assay  oz- 

ffecovery% 

Assay  oz 

7° 

•To 

/ 

£  76s.  per  fan  //?  0-?S?6  so/. 

2-O 

ftcf/ned  forpenftne,  0.4/6 
HanJKooct-cfTeosofe,/.^  • 
£uco/ypfus,            01  - 

34  3 

369 

43/0 

S/-8 

O-/4 

446 

J/ 

2 

/O   •       "        •     ~    OS-fa      • 

2-0 

Some 

37.3 

93-2 

3S-70 

60-9 

0-/0 

43  & 

J  3 

3 

/S  -     •     •    •  o-7S7o    • 

2.-0 

Same 

39.  / 

84-.  8 

3226 

863 

O-/O 

44-0 

3.6 

4 

2O   "      "      "      "    /-OO  ft,    • 

Z66 

Refined  fLfrpenf/ne,  0-3  /b. 
Hardwood-  creosote.  0-9  • 

SO-7S 

97  7S 

39  62 

88  & 

C-/4- 

296 

3S 

S 

+o  -   "    '  "  zootf,  ' 

/•S 

Creosofe,      /-4O  /6. 
Turpentine,    O-S4    " 
f/ne-o//,       o-oe    • 

70-  / 

96-Z<S 

SB.  34 

S3-S 

o-a2 

6-4 

.'•27 

results  with  the  use  of  as  low  as  two  pounds  of  sodium  sulphide  per 
ton  and  a  time  of  contact  with  the  ore  of  only  a  few  minutes. 

In  Table  III  are  two  similar  series  of  tests  on  ore  from  the  Scran- 
ton  mine  in  the  North  Tintic  district  of  Utah,  and  from  the  Wilbert 
mine,  in  the  Dome  district  of  Idaho.  While  the  Scranton  ore  gives  ex- 
cellent black  froth  of  good  grade  and  a  high  recovery,  it  is  difficult  to 
do  anything  with  the  Wilbert.  The  reason  for  this  was  never  quite 
apparent. 

In  Table  IV  is  shown  the  effect  of  time  of  contact  when  sulphidizing 
with  sodium  sulphide.  A  short  period  seems  satisfactory,  further 
time  decreases  the  recovery,  leaving  the  grade  of  the  concentrate  un- 
affected. In  test  No.  8,  an  oil  that  had  been  boiled  with  sulphur,  un- 
til its  smell  became  noticeably  bad,  gave  little  better  results  than  in 
other  tests  in  which  it  was  not  used. 

In  another  test  the  ore  was  agitated  with  sodium  sulphide  in  a 
Pachuca.  This  test  proved  that  the  air  oxidized  the  sodium  sulphide  to 


370 


FLOTATION 


sodium  sulphate  with  but  little  sulphidizing  of  the  ore,  and  on  further 
treatment  the  sulphidized  ore  re-oxidized.  Hence  it  seems  imperative 
that  the  treatment  with  sodium  sulphide  solution  must  be  without  any 
admixture  of  air.  The  simplest  machine  in  which  agitation  of  the 


Table  III 

<Sulph/c/iz/tiff     w/f/>    <Sod/um   <Su//on/de. 
•Scran  fon    Ore.      (Wo.  /.  2.3.  A  4.) 
Wi/derf    mi  II  -dump.     (Mo.  S.  6.  7,  4-6.) 

No. 

Socf/um  Su/ph/de 

Hours 

O/7  ;  pounds  per  ton 

Leoc/ 

Assay  % 

Recovery  % 

/ 

/2  /t>s  per  ton  in  0-6%  So/. 

'/a 

Mixture  of  refined  furpenf/ne  OS  /b.,cnd 
coo/  -for  creosofe     /-o  /b. 

6SS 

39-7 

<? 

2O     *        "       •'      -     /  O%     - 

/'/e. 

Coot-creosote.  0.36  /t>.       Cedor-o/7,  O-36  /b. 

29.  S 

30-4 

3 

40  ••                    a-o%   . 

a 

M/xfure  of  coo/-  fur  creosofe  /-a  /6s;  and 
refined  furpent/ne,  o-s  /6. 

S3-7 

9/2.    , 

4 

4O    •        -      '         2-O  %    " 

I 

M/xfure  of  cedar-  o/7,  refined  turpentine 
coo/-  far  creosofe,  and  ros/n;  S  /6s. 

66.6 

64--A 

S 

S   -              -     •     %% 

/& 

Af/xfure    of  crude    coa/-for,    /-S  /os. 
//o.  /seo  spec/a/  p/ne-o//  ,   O-6  /d. 

/6-S 

S&+ 

6 

/O    '         ••-     >/z%      . 

/a 

Spec/a/  pine-  for   o/V,    0-6  /£>. 

£73 

3/-3 

7 

/o  -       -            %><?{,    • 

3% 

M/xtt/re   of  ref/ned  furpenf/ne,   o-e  /6.  ,  and 
crude    coa/-far  creosofe     /-O  /d. 

J3./S 

79-4 

8 

SO    -              '     '    /0%    • 

2 

M/xfure  of  furpenfi/je  and  Se  C/g.  o-&/b>  and 
crude  coa/-far  creosote,   O-&  /6 

27-2 

S7-a 

relatively  coarsely  ground  ore  with  sodium  sulphide  solution  could 
take  place  without  having  an  excess  of  air  beaten  into  pulp,  would  be 
a  long  rotating  cylinder  like  a  cement-kiln,  rotated  only  fast  enough 
to  turn  over  the  charge  gently  without  entraining  air. 


Table     IV 
•Sodium   Sulphide   <Su/phid/'zinff 
Bu///on  Beck  s/ime-dump,   S-S%  /ecrd,  7-£o2..Si/ver,o.o£oi.Go/d. 

Ato. 

Jotf/urn  su/phkJe 

Hours 

O/'/i  pounds  per  ton 

Froth.  Ana/yses    fffKf  /fecoverffs. 

Lead 

•SS/ver 

Go/d 

Assay  % 

fteco*ery>& 

4ssqyaz 

/fecove/y% 

Assay  oz 

Sfeco*e/y% 

/ 

20  /6s.  perfon  /n  /%  so/ 

o-s 

Turpenf/ne,  /-O 

34-a 

747 

e/a 

36  4 

a 

/•o 

' 

35-0 

44  -S 

20-  / 

273 

4 



£.0 

. 

364 

46  3 

29.S 

38-7 

S 

4-O 

' 

346 

377 

282 

23  5 

6 

/6-S 

- 

330 

S94 

262 

36-0 

7 

Creosofe,   /-6 

/9-4 

6S4 

/Q-7 

460 

a 

40  •       •      •    •  e%  • 

170 

P/ne-nced/e  o//  softs- 
rcrfeo'  Mf/>  jt///oAur,  /•£ 

27  0 

637 

270 

54-2 

9 

/oo  •             •    •  s%  • 

aa-o 

Creosofe,  /-6 

20-0 

630 

/94 

46-6 

0  07 

60-6 

/O 

ao  •       •      •    •  /%  • 

24-0 

Turpenf/ne,  /•£ 

/3  / 

7O-O 

/3-4 

34  S 

OOS 

73-0 

// 



/7-0 

Creosofe  ,  /-6 

/9-4 

62-4 

/6-7 

46-0 

Table  V  contains  the  average  results  obtained  in  testing  various 
other  ores.  It  can  be  seen  that  some  ores  are  not  adapted  to  the  pro- 
cess of  sulphidizing  with  sodium  sulphide,  followed  by  flotation.  The 
ores  that  give  a  poor  recovery  contain  notable  amounts  of  acid-soluble 
alumina,  which  makes  them  clay-like.  A  number  of  ores  failed  to  give 
any  results  at  all — notably  the  slime  from  the  test-mill  of  the  Copper 
Queen  Consolidated,  whose  ore  has  a  different  geologic  association  from 


FLOTATION    OF    OXIDIZED    ORES 


371 


that  of  the  Shattuck-Arizona.  A  highly  colloidal  slime  from  the  mil] 
of  the  Mine  La  Motte,  in  Missouri,  is  also  difficult  to  treat.  Most  of 
these  refractory  ores  will  not  even  turn  black  with  amounts  of  sodium 
sulphide  that  have  been  successful  on  other  ores.  Whether  alumina 
reacts  with  sodium  sulphide  to  form  aluminates,  leaving  the  sulphur 
in  the  elemental  condition,  is  not  known,  but  this  might  afford  a  rea- 
sonable explanation.  Ores  containing  manganese  di-oxide  or  basic 
sulphates  of  iron  also  consume  sodium  sulphide  without  allowing  black- 
ening of  the  lead  carbonate. 

Sodium  sulphide  normally  costs  $30  to  $40  per  ton  at  Chicago. 
With  a  consumption  of  5  to  20  Ib.  per  ton  of  ore  it  can  be  seen  that  the 


Table     V 
•Sod/urn    •Su/phide   <Su/phid/z/ng 
M/sce/tcrneous    ores.       Average    re-su/fa- 

Ore 

Concentrates 

Recovery 

<Sod/um 
-Su/phidf 

T/fne 

M/ne 

Ana  fy  sis 

Pt>. 

Aff- 

Au. 

Pt>. 

d£ 

Au. 

f>(>. 

Ay.. 

Au 

% 

oz.. 

oz 

3| 

oz. 

oz. 

To 

<#> 

To 

/6s.  per  f  on 

Hours 

Cfi/ef  Con$o//'rfafed,  t/fcrh- 

28 

8-0 

87 

3/9 

6B 

45 

/o 

3  S 

Eureka  H/7/  dump,  (/fan. 

ao 

47 

002 

/4-O 

/69 

O-07 

40 

ao 

3O 

ao 

aao 

American  F/ap  ,     Ufa  :n 

42 

/e  /^ 

0-/9 

27  / 

2/6  O 

/33 

43 

48 

40 

/a 

3.0 

Bu///onvi//e  damp,  /Venxfo. 

9-07 

//•/<? 

o/o 

3S9 

14  8 

O-/6 

63 

46 

40 

6 

a  o 

Dry  Va//ey    dump,  Mevada 

7/S 

/004 

o-/o 

S78 

23  a 

O/O 

76 

27 

34 

ao 

so 

Ye//o*v  P/ne  ,    Nevada. 

/S-04 

//92 

46-3 

29-64 

89  a 

S/7 

ao 

/•as 

Onfar/o    damp,    IJfah. 

4-32 

9.44 

0.  04 

3a-S 

3S-78 

oaa 

ea 

45 

29 

ao 

ao 

Da/y  Wesf  dump,  Utah 

sas 

at  <•» 

o  oa 

927 

S970 

ooa 

/s 

44 

ao 

ao 

cost  of  such  sulphidizing  is  not  prohibitive.  In  fact,  it  is  necessary 
to  decant  some  of  the  solution  before  flotation  and  we  have  often  found 
that  not  all  of  the  sodium  sulphide  applied  to  the  ore  has  been  con- 
sumed, although  the  tables  of  results  give  the  sulphide  applied  to  the 
ore.  Hence  the  figures  given  in  the  tables  are  probably  the  maximum 
possible  consumptions  and  might  be  considerably  reduced  in  practice 
by  decanting  the  excess  of  unused  solution  before  flotation,  or  by  using 
less  sodium  sulphide  in  sulphidizing.  This  suggests  a  method  of  sul- 
phidizing  by  use  of  some  such  device  as  a  thickener  where  the  overflow 
solution  containing  sodium  sulphide  can  be  returned  to  the  feed  of  the 
thickener,  together  with  a  small  amount  of  a  strong  solution  of  new7 
sodium  sulphide.  We  have  determined  that  if  over  0.3%  of  alkalinity 
due  to  Na2S  is  left  in  the  water  in  which  the  sulphidized  ore  is  sus- 
pended, the  froth  is  too  tough  or  else  it  is  entirely  killed.  Hence,  the 
desirability  of  decanting  the  excess  of  sodium  sulphide  solution,  and 
re-pulping  with  fresh  water.  We  have  tested  the  overflow  solution  of 
sodium  sulphide  for  sulphidizing  new  ore  and  often  find  it  efficient. 


372  FLOTATION 

Sodium  sulphide  may  be  prepared  for  large-scale  use  by  the  reduc- 
tion of  sodium  sulphate  with  carbon.  This  is  the  usual  commercial 
method.  The  largest  use  of  sodium  sulphide  at  the  present  time  is  prob- 
ably in  the  tanning  industry.  When  prepared  for  shipment  it  is  usu- 
ally in  crystals  containing  a  considerable  amount  of  water  of  crystal- 
lization to  prevent  spontaneous  combustion.  Hence  the  market  brands 
of  '60%'  and  '30%'  usually  consist  of  only  60%  or  30%  Na,S  and  the 
remainder  is  mostly  water. 

The  poly-sulphides  of  sodium  did  not  prove  as  efficient  for  sulphi- 
dizing, whereas  the  sulph-hydrate  of  sodium,  NaSH,  seemed  to  be 
somewhat  more  efficient.  The  normal  sulphide  of  sodium  hydrolyses  to 
sodium  sulph-hydrate  and  sodium  hydroxide,  and  the  activity  of  so- 
dium sulphide  is,  for  that  reason,  probably  exactly  the  same  as  that  of 
the  sulph-hydrate,  although  the  presence  of  the  sodium  hydroxide  from 
hydrolysis  might  have  some  effect  on  the  efficiency  of  sulphidizing.  The 
poly-sulphides  of  sodium  can  be  prepared  commercially  by  boiling 
caustic  soda  with  powdered  sulphur  and  probably  consist  of  mixtures 
of  Na2S4  and  Na2S5.  We  hazard  the  guess  that  only  one  of  the  sulphur 
atoms  in  these  complex  molecules  is  acting  as  a  sulphide  sulphur,  the 
others  being  liberated  as  free  sulphur,  for  the  reason  that  some  of  the 
tests  showed  white  colloidal  sulphur  lining  the  bubbles  of  froth. 

In  consequence  of  the  above  mentioned  test- work,  carried  on  at  the 
University  of  Utah,  the  Prince  Consolidated  Mining  Company,  of  Pi- 
oche,  Nevada,  tested  the  process  further  in  its  application  of  two  old 
pan-amalgamation  tailing-dumps  at  Bullionville  and  Dry  Valley.  It 
was  found  that  practically  all  of  the  finely  powdered  lead  carbonate  in 
the  ore  could  be  extracted,  together  with  a  portion  of  the  silver  and 
gold  present.  This  resulted  in  the  erection  of  a  300-ton  mill.  The  ore 
contained  about  8.2%  lead  and  11  oz.  silver  per  ton,  together  with  about 
$1.40  worth  of  gold  per  ton.  The  finely  ground  tailing  is  excavated 
from  the  old  marsh  where  it  has  lain  for  about  20  years  and  is  then 
passed  through  a  tube-mill  to  break  up  the  lumps.  It  is  sulphidized  in 
a  round  wooden  tank  with  about  7  Ib.  of  sodium  sulphide  per  ton.  The 
agitator  in  this  sulphidizing-tank  is  the  regular  square-shaft  square- 
arm  agitator  used  in  a  number  of  Nevada  cyanide-mills  and  was  intro- 
duced by  the  engineer,  C.  F.  Sherwood,  who  designed  the  mill.  This 
was  installed  after  the  regular  Trent  agitator  (minus  the  air,  not  wish- 
ing to  oxidize  sodium  sulphide  and  the  ore  with  air  before  flotation) 
had  failed  to  give  satisfactory  sulphidizing.  About  one  half-hour  in 
the  sulphidizer  is  the  minimum  time.  The  ore  is  then  treated  for  flota- 
tion in  Callow  cells,  making  a  concentrate  containing  55%  lead. 


FLOTATION    OF    OXIDIZED    ORES  373 

The  recoveries  are:  lead  over  90%,  gold  45%,  silver  35%.  The 
tailing  from  the  six  Callow  roughing-cells  is  separated  in  a  Dorr  classi- 
fier into  sand  and  slime.  The  sand  is  treated  on  four  Deister  tables 
and  the  slime  is  mixed  with  more  oil  and  more  sodium  sulphide  and 
then  passed  through  two  Callow  cells,  which  make  a  middling  concen- 
trate and  a  finished  tailing.  The  middling  is  re-treated  with  the  orig- 
inal feed. 

After  a  short  time  the  feed  of  the  mill  began  to  contain  many  weeds 
from  the  old  roots  that  had  accumulated  from  the  growth  of  vegetation 
during  the  20  years.  The  froth  was  spoiled  and  not  until  some  sul- 
phuric acid  was  added  and  the  pulp  warmed  did  it  return.  The  pres- 
ent practice  is  to  add  sodium  sulphide  and  sulphuric  acid  together  in 
the  agitator,  and  the  mill  is  at  the  present  time  just  commencing  to  op- 
erate after  the  correction  of  these  various  unforseen  difficulties.  The 
concentrate  contains  only  about  15  to  20%  of  insoluble  but  on  being 
thickened  in  a  Dorr  tank  and  filtered  in  an  Oliver  filter  it  still  contains 
about  26%  of  moisture.  A  part  of  this  moisture  is  removed  in  a  dryer 
before  shipment. 

The  Shattuck-Arizona  Copper  Co.  is  now  preparing  to  build  a  sim- 
ilar mill  for  treatment  of  its  ores. 

The  work  at  the  Shattuck  caused  a  company  at  Kellogg,  Idaho,  to 
take  up  similar  work  on  a  local  lead-carbonate  ore.  It  was  found  that 
it  could  be  treated  successfully  and  a  40-ton  plant  is  now  in  operation. 
The  consumption  of  sodium  sulphide  is  occasionally  as  low  as  2  to  3 
Ib.  per  ton.  R.  S.  Handy  is  responsible  for  the  success  of  this  work. 

CALCIUM  SULPHIDES  are  more  sluggish  in  their  action  than  the  cor- 
responding sulphides  of  sodium.  Again  we  find  the  sulph-hydrate  of 
calcium  more  active  than  the  sulphide,  which  in  turn  is  more  active 
than  the  poly-sulphide.  But  for  ease  of  preparation  at  the  mill  the 
poly-sulphide  takes  precedence.  It  is  obtained  by  boiling  slaked  lime 
with  powdered  sulphur  for  two  to  five  hours  and  is  extremely  soluble, 
while  the  normal  sulphide  of  calcium  is  only  slightly  soluble.  The  nor- 
mal sulphide  can  be  obtained  by  reducing  gypsum  with  carbon  at  high 
temperature. 

The  results  of  a  few  tests  with  the  poly-sulphide  on  the  May  Day 
ore  (Tintic  district)  are  contained  in  Table  VI.  The  work  done  with 
sodium  sulphide  is  superior  to  that  done  with  calcium  sulphide.  There 
are  places  where  the  use  of  calcium  poly-sulphide  might  be  advantag- 
eous or  even  necessary,  either  alone  or  in  combination  with  sodium  sul- 
phide. Some  slimes  are  deflocculated  by  sodium  sulphide  so  that  it  is 
difficult  to  make  them  settle.  The  use  of  calcium  poly-sulphide  will 


374 


FLOTATION 


have  the  opposite  effect  and  the  proper  mixture  of  the  two  might  be 
used  to  control  the  settling  of  the  sulphidized  slime. 

The  other  methods  of  sulphidizing,  such  as  the  use  of  sulphur  vapor 


Table    VI. 

Sutphid/z/ng    with  <so/uf/ons   of    Cafe/urn    Po/y~<su/ph/de. 
May  Day  ore.     ^.S^  /eac/,  end  2.8  oz.  s/'/ver  per  fan. 
O//s  ••    coo/-  creosote,  /  B  /6s.  per  fon  ;    turpentine,  O-4-  /b.  per  fon. 

Wo. 

Hours 

Froth 

(pounds  per  fan) 

Lead 

S/fver 

Assay  °& 

Recovery  % 

Assay  oz. 

Recovery  9£ 

/ 

/•6 

6 

/2-S 

32  2 

a 

a.o 

/•S 

/6-4 

ao-7 

3 

/6-0 

3-6 

B6-/ 

73.0 

//•Sff 

48 

on  heated  ore,  colloidal  sulphur  solutions,  and  sulphuretted  flotation- 
oil,  have  not  proved  technically  successful  or  adaptable,  according  to 
our  experiments  with  lead-carbonate  ores. 

OXIDIZED  COPPER  ORES.  Many  attempts  have  been  made,  both  by 
large  operating  companies  and  by  other  experimenters,  to  float  the  car- 
bonate and  other  oxidized  minerals  of  copper.  For  that  reason  the 
testing  of  such  ores  by  us  has  been  limited. 

Hydrogen  sulphide  seems  to  be  by  far  the  best  medium  for  sulphid- 
izing  oxidized  copper  ores  previous  to  flotation.  When  applied  to  the 
dry  ores  we  found  the  same  conditions  as  those  mentioned  for  lead; 
the  particles  are  sulphidized  to  the  centre,  which  requires  an  excesssive 
amount  of  hydrogen  sulphide.  Applied  to  the  wet  pulp,  the  hydrogen 
sulphide  seems  to  cause  true  filming.  Our  work  has  yielded  a  black 
concentrate,  but  we  are  informed  by  J.  M.  Callow,  of  the  General 
Engineering  Co.,  that  the  company  has  been  able  to  reduce  the  amount 
of  sulphur  used  to  a  point  where  the  froth  is  green  with  slightly  coated 
malachite.  He  states  that  as  little  as  half  a  pound  of  sulphur  per  ton 
of  ore  is  giving  good  extractions  in  the  plant  of  the  Magma  Copper 
Co.,  at  Magma,  Arizona,  where  his  company  has  put  in  the  first  suc- 
cessful installation  of  this  kind. 

Sodium  sulphide  has  been  tested  by  a  number  of  the  larger  com- 
panies that  have  oxidized  copper  minerals  in  their  sulphide  ores.  The 
amount  of  oxidized  copper  in  such  ores  is  usually  a  fraction  of  1%, 
so  that  only  two  or  three  pounds  of  sodium  sulphide  per  ton  of  ore  is 
necessary.  This  is  usually  added  to  .the  machines  during  flotation, 


FLOTATION    OF    OXIDIZED    ORES  375 

or  to  the  mixing-tanks  before  flotation.  Our  experience  is  that  if  some 
little  time  of  preliminary  contact  is  allowed  before  flotation  is  at- 
tempted, better  sulphidizing  of  the  material  will  result. 

Calcium  poly-sulphide  has  been  used  for  some  time  in  a  number  of 
the  large  copper-concentrating  mills  with  indifferent  success,  and  seems 
to  be  detrimental  in  some  instances.  On  the  ores  tested  by  us  fair  re- 
sults were  obtained  if  the  calcium  poly-sulphide  was  allowed  to  act 
until  the  ore  had  become  well  blackened. 

It  is  stated  that  sulphur  vapor  was  tested  at  one  of  the  large  plants 
for  flotation  of  oxidized  forms  of  copper  and  gave  better  results  than 
any  other  methods  of  sulphidizing.  Of  course  this  method  has  the  dis- 
advantage of  having  to  be  applied  to  dried,  heated,  and  finely  divided 
ore. 

Sulphuretted  oils  are  being  used  at  a  number  of  plants  to  supple- 
ment other  methods  of  sulphidizing  and  considerable  secrecy  is  ob- 
served as  to  the  technical  details  of  this  work.  During  a  recent  visit 
of  the  Utah  section  of  the  American  Institute  of  Mining  Engineers  to 
the  Arthur  mill  of  the  Utah  Copper  Co.,  the  strong  smell  in  the  air 
elicited  the  information  that  the  flotation  unit  of  1000  tons  daily  ca- 
pacity was  receiving  a  flotation-oil  that  had  been  previously  distilled 
with  sulphur. 

So  far  as  we  are  aware  colloidal  sulphur  does  not  assist  in  the  flota- 
tion of  oxidized  forms  of  copper.  Neither  has  the  silicate  of  copper 
been  successfully  floated  by  sulphidizing  flotation.  It  will  blacken 
when  sulphidized,  but  it  resists  flotation.  Possibly  it  still  presents  a 
silicate  surface  rather  than  a  sulphide  surface.  For  this  reason, 
most  of  the  large  copper  companies  in  Arizona  have  been  considering 
the  leaching  of  oxidized  copper  from  their  tailing  rather  than  lose  the 
silicate  copper  that  may  be  present. 

Another  difficulty  has  arisen  from  attempts  to  recover  both  the  ox- 
idized and  sulphide  copper  simultaneously  from  partly  oxidized  ores. 
Throughout  Arizona  and  New  Mexico  the  larger  companies  have  at- 
tempted sulphidizing  of  the  oxidized  copper  followed  by  flotation  of 
the  natural  and  the  artificial  sulphides  together.  In  almost  every  case 
they  have  failed  because  the  flotation  of  the  natural  sulphides  seems 
to  be  spoiled  by  the  conditions  that  are  Best  for  the  artificial  sulphides. 
A  similar  experience  is  recorded  by  the  Anaconda  Copper  Co.  Only  at 
Chino  has  this  difficulty  been  mastered,  through  the  efforts  of  0.  Wiser. 
The  product  being  treated  is  the  vanner-concentrate,  which  con- 
tains considerable  oxidized  copper.  It  is,  of  course,  desirable  to  clean 
the  vanner-concentrate  in  order  to  put  the  iron  and  silica  into  a  self- 


376  FLOTATION 

fluxing  ratio  for  the  smelter.  This  could  not  be  done  it'  the  oxidized 
copper  could  not  be  floated.  At  first,  the  sulphidizing  reagents  caused 
the  natural  sulphides  to  drop  out  of  the  froth  in  this  plant,  as  in  many 
others,  and  for  a  time  the  natural  sulphides  were  floated  out  first  be- 
fore the  sulphidizing  reagents  were  added,  but  finally  the  proper  mix- 
ture of  chemical  and  oil  was  found  to  float  them  simultaneously.  One 
of  the  principal  ingredients  is  a  solution  of  sodium  resinate  prepared 
by  dissolving  resin  in  a  solution  of  caustic  soda.  This  stiffens  the 
froth.  The  froth  is  red  with  magnetite  and  hematite,  which  float  with 
the  copper  minerals.  The  sodium  resinate  solution  is  used  at  several 
mills. 

The  plant  at  Chino  is  further  along  in  the  successful  treatment  of 
semi-oxidized  copper  ores  than  any  of  the  other  mills  in  the  South- 
west. Sulphidizing  of  the  whole  mill-feed  is  not  yet  allowable  on  ac- 
count of  the  large  quantities  of  sulphidizers  necessary.  Only  the  van- 
ner-concentrate  is  being  sulphidized  with  sodium  sulphide.  However, 
an  experimental  unit  of  one  to  two  tons  capacity  is  also  used.  The 
crushed  ore  for  this  testing-plant  is  tube-milled  and  then  tabled  to  re- 
move the  coarse  concentrate ;  after  that  it  is  treated  in  an  agitator  with 
sulphuric  acid  amounting  to  3  Ib.  per  pound  of  oxidized  copper  pres- 
ent. This  dissolves  all  the  copper,  including  the  silicate.  On  passing 
the  pulp  through  a  ball-mill  filled  with  scrap-iron  the  copper  in  solu- 
tion is  cemented  and  issues  with  the  pulp  from  the  tube-mill.  The 
greater  portion  of  the  copper  is  now  ready  for  flotation  without  any 
oiling.  The  smell  of  hydrogen  is  strong  and  it  is  the  opinion  of  the 
metallurgist  in  charge  that  the  reaction  of  the  acid  on  the  iron  liberates 
hydrogen  and  hydro-carbons  from  the  cast-iron  used  and  that  these 
hydro-carbons  are  partly  oiling  the  cement  copper  formed.  However, 
on  passing  to  the  flotation  machine  some  tar  and  coal-creosote  are 
necessary  in  order  to  get  a  high  extraction  of  the  natural  sulphides 
and  the  cement  copper  together.  It  is  said  that  trouble  was  experi- 
enced in  getting  a  good  froth  with  this  material. 

This  process  is  being  considered  by  others,  notably  the  Miami  and 
the  Inspiration  companies.  It  has  been  patented  by  Dr.  Rudolf  Gahl 
in  U.  S.  1,217,437. 

One  question  to  be  considered  in  the  use  of  such  a  process  is 
whether  or  not  substances  like  iron  sulphate  will  accumulate  in  the  so- 
lution to  a  point  where  they  will  injure  flotation.  It  is  known  that  a 
small  amount  of  ferrous  sulphate  or  of  copper  sulphate  in  solution  i?'. 
deleterious.  As  most  of  the  Arizona  mills  find  it  necessary  to  operate 
in  closed  circuit  this  question  of  contamination  of  mill-water  is  iinpor- 


FLOTATION    OF    OXIDIZED    OEES  377 

taut.  It  is  not  impossible  that  the  addition  of  a  little  lime  to  the  tail- 
ing, as  it  flows  from  the  mill,  would  throw  out  most  of  the  iron  and 
other  metals  so  that  the  water  returned  from  the  tailing-pond  would 
not  be  contaminated. 

The  Detroit  Copper  Co.  is  known  to  be  experimenting  with  sul- 
phide-filming of  copper  carbonate  ores.  A  visit  to  the  test-mill  at  Bis- 
bee  showed  an  acid-tower  used  for  the  preparation  of  a  solution  of 
hydrogen  sulphide,  which  was  generated  from  iron  matte  and  sul- 
phuric acid.  The  copper  ore  was  being  treated  with  this  solution,  in 
round  tanks  with  mechanical  agitators,  for  a  number  of  hours  before 
passing  to  the  flotation-machines  of  the  Rork-Kraut-Kohlberg  type. 
Laboratory  work  had  previously  shown  an  excellent  recovery  and  the 
details  of  larger-scale  practice  were  being  worked  out  at  the  time  of  the 
visit  (September  20,  1916). 

An  interesting  paper  by  M.  H.  Thornberry  was  published  in  the 
Bulletin  of  the  Rolla  School  of  Mines,  Vol.  3.  No  1.  A  soap,  called 
Naphtha  Powder,  manufactured  by  Peet  Bros.,  was  used  at  the  rate 
of  two  pounds  per  ton  of  ore,  with  a  6.5:1  water:  solid  ratio.  A 
minute  amount  of  oleic  acid  was  added.  The  ore  contained  both  sul- 
phides and  oxidized  minerals  of  copper  and  assayed  2.95%  total 
copper,  of  which  2.34%  was  oxidized. 

A  number  of  Thornberry 's  tests,  re-calculated  to  eliminate  losses  of 
weight,  show  the  following  recoveries  when  treated  by  flotation  under 
the  above  conditions : 

/ —    — Percentages  of  recovery —   — N 
Test  Oxidized          Sulphide       Total  copper 

4 61.0  92.1  72.1 

5    63.8  93.0  75.1 

6    68.7  89.6  76.6 

He  offered  the  following  conclusions: 

(1)  With  rain  or  distilled  water  this  process  can  be  used  to  ad- 
vantage. 

(2)  Water  containing  sulphates  will   prevent  carbonates  from 
floating. 

(3)  Water  containing  chlorides  will  prevent  the  carbonates  from 
floating,  but  this  difficulty  can  be  overcome  by  the  addition  of  sodium 
carbonate. 

, Thornberry  is  the  only  person  who  has  reported  much  success  with 
the  use  of  soaps  in  the  flotation  of  sulphide  ores.  It  is  possible  that  dif- 
ferent effects  are  involved  when  oxidized  ores  are  considered.  Evi- 
dence is  accumulating  to  show  that  it  is  possible  to  make  certain  or- 
ganic acids  form  combinations  with  heavy  metals  present  as  carbonates 


378  FLOTATION 

in  the  ore.  The  soap  is  known  to  hydrolyze  in  dilute  solutions  and  it  is 
entirely  possible  that  the  liberated  fatty  acids  have  combined  super- 
ficially with  the  copper-carbonate  particles  sufficiently  to  'oil'  them  for 
flotation.  The  use  of  sodium  resinate  in  the  flotation  of  copper  car- 
bonates at  Chino  has  already  been  mentioned.  Sodium  resinate  is 
nothing  but  a  resin-soap.  The  resin  acids  are  not  so  well  known  to  met- 
allurgists as  are  oleic,  palmitic,  stearie,  and  other  acids,  whose  sodium 
salts  form  the  principal  ingredients  of  soap.  A  study  of  the  action  of 
these  organic  acids  on  minerals  is  desirable. 

Some  excellent  data  on  use  cf  hydrogen  sulphide  for  sulphide-film- 
ing of  copper  carbonate  have  been  published  by  J.  M.  Callow  in  a 
paper  abstracted  elsewhere  in  this  book. 

OXIDIZED  ZINC  MINERALS.  So  far  as  we  know  no  one  is  successful  in 
the  flotation  of  oxidized  ores  of  zinc.  Our  results  are  absolutely  nega- 
tive. We  are  informed  that  some  headway  was  made  with  the  prob- 
lem by  F.  W.  Traphagen  and  one  of  his  students,  at  the  Colorado 
School  of  Mines,  but  the  sulphide  film  seemed  to  come  off  easily.  Poor 
results  were  obtained,  whatever  the  cause.  Only  Bacon  claims  any  suc- 
cess in  this  line  and  his  method  is  to  get  the  zinc  into  solution  in,  say, 
the  sulphate  form,  followed  by  precipitation  of  zinc  sulphide  by  the 
use  of  an  alkaline  sulphide,  with  subsequent  flotation  from  the  sulphi- 
dized pulp— at  least  his  patent  claims  as  much.  There  are  few  places, 
however,  where  sulphuric  acid  and  sodium  or  calcium  sulphides  could 
be  obtained  cheaply  enough  to  allow  of  the  application  of  this  process. 

We  have  recently  been  informed  by  Frank  A.  Bird,  of  Salt  Lake 
City,  that  he  has  obtained  some  success  in  the  flotation  of  a  zinc-car- 
bonate ore,  by  using  the  idea  seemingly  underlying  Thornberry's 
work.  After  many  of  the  ordinary  flotation-oils  had  failed  to  do 
anything  with  sulphidized  or  non-sulphidized  ore,  oleic  acid  was  added 
to  an  ore-sample  while  being  sulphidized  with  sodium  sulphide.  The 
result  was  a  fair  grade  of  concentrate  and  about  50%  recovery. 
Whether  the  sulphur  in  the  sodium  sulphide  had  anything  to  do  with 
it  or  whether  alkalinity  was  all  that  was  necessary,  was  not  determined. 

OTHER  MINERALS.  Flotation  on  a  commercial  scale  seems  to  be 
possible  only  after  sulphidizing.  We  are  not  certain  but  that  cuprite 
and  similar  minerals  of  highly  developed  cleavage  or  crystalline  char- 
acter can  be  floated  direct  without  sulphidizing.  From  private  parties 
we  hear  of  laboratory  successes  in  the  flotation  of  scheelite,  fluorite, 
and  similar  minerals.  The  flotation  of  magnetite  seems  well  estab- 
lished. J.  T.  Terry,  in  a  paper  re-printed  in  this  book,  also  reports 
the  successful  sulphidizing  of  cassiterite,  followed  by  flotation. 


FLOTATION    OF    GOLD    AND    SILVER  379 

THE  FLOTATION  OF  GOLD  AND  SILVER  MINERAL 

By  T.  A.  RICKARD 
(From  the  Mining  and  Scientific  Press  of  August  25,  1917) 

In  the  title  to  this  article  I  have  avoided  the  use  of  the  word  *  ore, ' 
because  the  object  of  flotation  is  to  float  not  the  'ore'  but  the  valuable 
mineral  in  the  ore,  leaving  the  gangue  to  sink.  It  is  a  selective  process, 
based  upon  the  idea  that  the  ore  consists  of  valuable  and  of  valueless 
components,  which  must  be  separated  so  that  the  valuable  component 
may  be  concentrated  as  cleanly  as  possible  previously  to  a  final  treat- 
ment in  which  the  metal  or  metals  are  extracted  and  prepared  for  the 
market. 

Some  of  the  earliest  work  in  flotation,  such  as  that  at  the  Glasdir 
mine,  in  1896-1899,  was  done  on  an  ore  containing  gold  and  silver,  but 
the  recovery  of  the  precious  metals  was  incidental  to  the  concentration, 
of  the  chalcopyrite  with  which  they  were  intimately  associated.  Like- 
wise the  saving  of  the  silver  in  the  Broken  Hill  ore  was  incidental  to 
the  recovery  of  the  sulphides  of  lead  and  zinc.  In  such  cases — and 
they  are  typical — the  floatability  of  gold  and  silver  in  the  native  state, 
or  of  their  mineral  compounds,  does  not  present  any  special  problem 
because  the  recovery  of  the  gold  and  silver  follows  the  concentration 
of  the  base-metal  sulphides  by  which  they  are  usually  so  closely  ac- 
companied in  ore  deposits.  However,  the  floatability  of  native  gold, 
as  of  native  silver,  hardly  needs  special  demonstration  here.  'Float 
gold'  has  been  a  bugbear  of  processes  in  which  water  is  used,  whether 
in  the  sluice-box  of  the  gulch  or  in  the  stamp-mill  on  the  hillside. 
Small  particles  of  gold,  particularly  when  flaky,  are  easily  transported 
011  water,  as  every  miner  has  learned  to  his  sorrow.  The  platy  form 
of  gold,  so  common  in  veins,  lends  itself  readily  to  flotation,  if  the 
particles  are  small,  by  offering  a  large  surface  to  the  play  of  surface- 
tension  and  to  the  adhesion  of  air.  The  high  metallic  lustre  of  gold 
is  a  characteristic  that  experience  in  flotation  would  lead  us  to  associate 
with  easy  buoyancy  in  the  presence  of  air  and  of  oil.  If  the  gold  is 
'  rusty, '  that  is,  coated  with  iron  oxide  or  with  manganese  di-oxide,  or, 
as  more  rarely  happens,  with  a  film  of  silica,  we  should  not  expect  it  to 
float,  as  we  should  not  expect  it  to  amalgamate  or  to  cyanide  freely, 
until  it  had  undergone  such  abrasion  as  would  expose  a  fresh  clean 
surface.  Similarly  gold  in  a  clayey  ore  may  make  trouble  for  any 
process  in  which  water  is  used,  but  this,  like  the  Crustiness/  is  nothing 
new  and  is  not  peculiar  to  flotation. 


380  FLOTATION 

As  regards  silver,  the  same  general  ideas  apply.  Silver  in  flaky 
form  is  elusive  when  running  water  is  used,  because  it  is  readily 
floated ;  likewise  when  it  presents  a  clean  surface  it  is  easily  amenable 
to  the  guidance  of  the  ascending  bubbles.  One  would  expect  native 
silver  and  those  of  its  compounds  that  are  either  highly  lustrous,  or 
have  a  marked  cleavage,  to  float  easily.  This  is  a  fact.  Experiments 
made  at  Cobalt*  showed  a  recovery  of  92  to  97%  for  metallic  silver, 
77  to  89%  for  argentite,  85  to  87%  for  pyrargyrite,  78  to  80%  for 
proustite,  and  69%  for  frieslebenite.  These  experimental  results  have 
been  confirmed  in  practice,  a  recovery  of  96%  having  been  made  by 
using  oil-flotation  to  supplement  gravity-concentration,  t  Of  man- 
ganiferous  silver  ores,  a  type  familiar  to  the  Mexican  miner,  it  can  be 
stated  that  when  they  cannot  be  cyanided  they  also  cannot  be  floated. 
The  obstacle  probably  is  the  double  oxide  of  silver  and  manganese. 
Even  preliminary  sulphidization  appears  ineffective  because  the 
sodium  sulphide  will  not  attack  the  manganese-silver  compound. 

As  regards  the  economic  gold  minerals,  namely,  the  tellurides,  they 
are  so  lustrous  that  one  would  expect  them  to  be  eminently  floatable. 
That  would  apply  to  the  silver  tellurides  also.  Such  has  been  the 
experience  at  Cripple  Creek,  provided,  of  course,  that  oxidized  ore  is 
carefully  excluded  from  the  mill-feed.  At  the  Vindicator  mine  the 
practice  is  to  wash  the  oxidized  material  out  of  the  ore  before  it  goes 
to  the  flotation  plant.  At  the  mines  on  the  Mother  Lode,  in  California, 
where  the  carbonaceous  slate  causes  trouble  by  re-precipitation  of  gold 
in  the  cyanide  solution,  it  has  been  found  advantageous  to  apply 
flotation  after  amalgamation. 

However,  even  if  sundry  gold  and  silver  minerals  will  float,  that 
does  not  mean  that  they  can  be  recovered  successfully  as  a  concen- 
trate by  the  frothing  process.  Direct  floatability  would  refer  to  the 
surface-tension  methods,  such  as  those  of  Wood  and  Macquisten. 

For  the  success  of  the  older  methods,  such  as  that  introduced  by 
the  Minerals  Separation  company,  employing  mechanical  agitation,  it 
is  necessary  that  the  pulp  should  contain  finely  divided  mineral  able 
to  pass  into  the  oil-water  interface  and  in  quantity  sufficient  to  stabil- 
ize the  air-bubbles  by  armoring  them.  Thus,  a  clean  gold-bearing 
quartz  is  unsuitable  to  a  machine  working  on  the  principle  of  violent 
agitation  unless,  of  course,  it  contain  enough  gold,  so  sub-divided  by 


*Canadian  Mining  Institute.  Bull.  No.  62.  J.  M.  Callow  and  E.  B. 
Thornhill. 

fAt  Cobalt  the  flotation-cell  has  replaced  the  slime-table  in  the  McKinley- 
Darragh  mill,  while  in  the  Nipissing,  Buffalo  Mines,  and  Dominion  Reduction 
mills  the  cyanidation  of  tailing  has  given  way  to  re-grinding  and  flotation. 


FLOTATION    OF    GOLD    AND    SILVER  381 

the  time  it  reaches  the  flotation-cell  as  to  suffice  for  froth-making. 
The  tailing  from  a  vanner  is  not  as  suitable  for  the  agitation-froth 
process  as  the  pulp  before  it  has  undergone  concentration  on  the 
vanner.  Similarly,  a  gold-quartz  ore  containing  5%  gold-bearing 
pyrite  or  other  sulphides  is  better  adapted  to  agitation-frothing  than 
one  containing  1%  only.  This  applies  to  the  mechanical  stirrer;  it 
does  not  apply  to  the  pneumatic  machine,  in  which  air-bubbles,  sup- 
plied lavishly,  rise  quietly  through  the  pulp.  In  such  a  machine  it  is 
not  necessary  to  have  a  large  "proportion  of  mineral  for  stabilizing 
the  froth  because  the  plentiful  supply  of  bubbles  obviates  that  re- 
quirement. As  one  bubble  breaks,  another  is  ready  to  take  its  place, 
so  that  the  float,  or  concentrate,  does  not  fall,  but  is  lifted  successively 
until  it  passes  over  the  lip  of  the  cell. 

Another  important  phase  of  the  subject  is  the  recovery  of  the  base 
metals  associated  with  the  precious  metals.  In  mills  using  amalgama- 
tion and  cyanidation,  the  presence  of  base-metal  sulphides  may  be  so 
detrimental  that  an  ore  containing  any  considerable  percentage  of 
them  is  likely  to  be  left  in  the  mine.  In  some  cases  the  presence  of 
base-metal  sulphides,  insufficient  to  be  a  source  of  revenue,  but  suffi- 
cient to  interfere  with  the  milling,  has  rendered  it  unprofitable  to 
treat  an  ore.  For  such  mines  the  use  of  flotation  comes  as  a  real  boon. 
In  the  San  Juan  region  of  Colorado  at  this  time  there  is  a  pronounced 
growth  of  productive  activity  because  flotation  has  facilitated  the  re- 
covery of  the  base  metals  associated  with  the  precious,  and  so  long  as 
the  metal  markets  remain  propitious,  we  may  expect  a  further  expan- 
sion in  this  direction.  Flotation  is  superior  to  any  of  the  older  wet 
processes — amalgamation,  chlorination,  and  cyanidation — in  that  it 
will  enable  the  miner  to  recover  not  gold  and  silver  only,  but  copper, 
lead,  and  zinc  as  well. 

These  general  remarks  will  serve  to  introduce  some  analyses  of 
specific  conditions — a  more  satisfactory  method  of  discussing  a  prob- 
lem that  is  economic  as  well  as  scientific. 

NORTH  STAR.  Early  in  1916  the  management  of  the  North  Star 
Mines,  at  Grass  Valley,  undertook  a  critical  analysis*  of  the  milling 
methods  then  in  use,  with  a  view  to  consolidating  the  existing  plants 
and  obtaining  greater  economy  of  treatment.  The  ore  was  being  re- 
duced in  two  40-stamp  mills,  each  with  a  cyanide  annex,  situated  at  the 
two  main  openings  of  the  mine.  The  combined  capacity  of  the  two 
plants  was  110,000  tons  per  annum,  development  work  during  1915  had 


*For  this  information  I  am  indebted  to  William  Hague,  managing  director 
of  the  North  Star  Mines. 


382  FLOTATION 

been  highly  successful,  and  it  was  anticipated  that  by  centralizing  the 
entire  plant  at  one  shaft  a  considerable  saving  in  operating  expense 
might  be  made. 

The  ore  was  being  crushed  by  1050-lb.  stamps  to  pass  20-mesh 
screens,  the  treatment  involving  amalgamation  in  the  mortars  and  on 
plates,  then  table  concentration,  followed  by  classification  into  sand 
and  slime  for  separate  cyanidation.  The  concentrate  was  re-ground  in 
tube-mills  to  pass  200-mesh  and  treated  in  the  slime-plant.  The  total 
extraction  averaged  $10  in  gold  per  ton  of  ore;  of  this,  $5  was  ob- 
tained in  the  stamp-mortars,  $3  on  the  amalgamating  plates,  and  $2 
from  the  concentrate,  sand,  and  slime.  The  tailing  averaged  25  to  35 
cents  per  ton,  so  that  the  extraction  averaged  97%.  To  treat  108,000 
tons  in  1915  the  cost  of  milling  was  $51,000,  for  cyanidation  $42,000, 
a  total  of  $93,000,  besides  the  tailing-loss  of  $30,000— a  total  deduc- 
tion of  $123,000. 

Whatever  process  might  be  adopted,  it  was  deemed  advisable  to 
retain  amalgamation,  since  fully  50%  of  the  gold  extracted  was 
caught  in  the  mortars  and  30%  on  the  plates.  It  seemed  wise  to  use 
amalgamation  to  catch  as  much  of  the  free  gold  as  possible  early  in 
the  operations,  as  a  sportsman  tries  to  shoot  his  bird  with  the  first 
barrel  rather  than  the  second. 

The  necessary  experiments  in  flotation  were  made  by  the  firm  of 
Hamilton,  Beauchamp  &  Woodworth,  of  San  Francisco.  Samples  of 
plate-tailing  were  sent  to  them.  The  assay-value  of  these  samples 
ranged  from  $2.50  to  $2.90  in  gold  per  ton.  The  first  tests  indicated 
that  the  material  required  re-grinding,  to  pass  80-mesh,  in  order  to 
obtain  a  good  recovery  in  the  flotation-cell.  When  the  heading  assayed 
$2.50  the  residue  from  these  tests  ranged  between  10  cents  per  ton 
on  pulp  ground  to  200-mesh,  and  40  cents  on  pulp  reduced  to  pass 
65-mesh.  When  the  plate-tailing  was  ground  to  pass  80-mesh  the 
flotation  residue  averaged  25  to  30  cents  per  ton,  like  the  residue  after 
cyanidation. 

The  treatment  of  the  flotation  concentrate  was  the  next  step  in 
the  investigation.  To  ship  the  concentrate  to  a  smelter — the  Selby 
smelter,  near  San  Francisco — would  cost  $17  per  ton,  for  sacking, 
haulage,  freight,  treatment,  and  losses.  This  cost,  on  an  ore  contain- 
ing 3J%  sulphides,  would  mean  50  cents  per  ton  of  ore.  Smelting 
therefore  was  not  to  be  recommended.  There  remained  the  possibility 
of  cyaniding  the  concentrate.  The  ratio  of  concentration  being  30  to 
1,  the  flotation  product  was  worth  from  $70  to  $90  per  ton.  The 
residue  from  the  working-tests,  when  cyaniding  the  flotation  concen- 


FLOTATION    OF    GOLD    AND    SILVER  383 

trate,  averaged  $6  per  ton.  The  average  consumption  of  cyanide  was 
6  Ib.  per  ton.  Experiments  were  made  also  to  learn  what  effect  the 
flotation-oil  had  on  the  precipitation  of  the  gold  or  on  the  fouling  of 
the  cyanide  solution.  The  results  indicated  that  no  difficulty  was  to 
be  anticipated  from  the  presence  of  small  quantities  of  oil  in  the  con- 
centrate, i  r  i  ^fj 

Given  the  results  of  these  flotation  experiments  and  comparing 
them  with  the  results  obtained  in  cyanide  practice,  it  appeared  that 
three  methods  were  available  for  use  in  the  consolidated  plant  which 
was  to  treat  110,000  tons  per  annum: 

No.  1.  To  use  60  stamps  of  1500  Ib.  each  and  crush  to  0.04  inch 
diameter,  employing  amalgamation,  classification,  concentration  of  the 
sand,  the  classifier  overflow  and  the  concentrator  tailing  each  going 
by  separate  conduits  to  the  cyanide  plant;  the  concentrate  to  be  re- 
ground  to  200-mesh  and  to  undergo  separate  treatment  in  the  cyanide 
annex,  in  order  to  ensure  sufficient  contact  with  the  solution  before 
being  delivered  to  the  slime-plant. 

No.  2.  To  use  40  stamps  of  1500  Ib.  each,  crushing  to  8-mesh, 
followed  by  amalgamation,  classification,  and  re-grinding ;  to  re-grind 
70%  of  the  stamp-product  in  tube  or  ball-mills  to  pass  80-mesh,  this 
product  to  be  treated  by  flotation,  re-grinding  the  flotation  concen- 
trate to  200-mesh  before  cyaniding  it. 

No.  3.  The  same  as  No.  1  except  that,  instead  of  cyaniding  the 
slime,  to  treat  everything  finer  than  150-mesh  by  flotation  and  to  leach 
the  coarser  material  with  cyanide  solution;  the  flotation  concentrate 
to  be  cyanided  with  the  re-ground  product  of  the  water-concentrators. 

Tests  made  in  the  mill  showed  that  the  1500-lb.  stamp  falling  6 
inches  105  times  per  minute  would  crush  a  little  more  than  5  tons  per 
day  to  0.04  inch,  the  screen  having  an  open  area  of  36% ;  and  also 
that  this  weight  of  stamp,  crushing  to  8-mesh,  would  have  a  duty  of 
7£  tons,  yielding  a  product  70%  of  which  would  be  coarser  than 
80-mesh. 

The  question  of  using  ball-mills,  both  as  primary  and  secondary 
crushers,  had  to  be  considered.  The  fact  that  50%  of  the  gold  could 
be  saved  in  the  mortars  was  favorable  to  the  retention  of  the  stamps. 
Furthermore,  in  referring  to  descriptions  of  South  African  practice, 
it  was  noted  that  from  5  to  10%  less  gold  was  recovered  by  amalgama- 
tion after  coarse  crushing  followed  by  tube-milling  was  introduced. 
If  5%  more  of  the  gold  in  the  North  Star  ore,  formerly  saved  by 
amalgamation,  were  thrown  into  the  cyanide  annex,  the  extra  loss  in 
cyanidation  would  off-set  the  saving  of  power  and  supplies  to  be 
anticipated  from  the  substitution  of  ball-mills. 


384  FLOTATION 

In  estimating  the  operating  cost  of  the  60-stamp  mill  and  cyanide 
annex,  the  management  was  able  to  supplement  its  own  experience 
with  that  of  a  neighboring  plant  having  a  capacity  equal  to  that  of  the 
one  being  planned.  In  estimating  the  cost  of  flotation  treatment,  the 
North  Star  management  was  less  confident,  having  to  depend  largely 
upon  the  advice  of  others;  but  by  giving  due  weight  to  the  evidence 
available  it  was  possible  to  come  to  a  fairly  trustworthy  conclusion, 
namely : 

No.  1  method,  applied  to  110,000  tons  in  one  year,  involved  a 
working  cost  of  $75,000,  plus  a  tailing-loss  of  $33,000,  making  a  total 
deduction  of  $108,000. 

No.  2  would  require  a  working  cost  of  $69,000  on  the  same  tonnage 
and  in  the  same  time,  plus  a  tailing-loss  of  $27,000,  plus  a  loss  of 
$20,000  more  (3300  tons  of  flotation  concentrate  per  annum  in  which 
$6  per  ton  would  be  left  after  cyanidation)  in  the  residue  of  flotation 
concentrate  after  cyanidation.  The  total  deduction  would  be  $116,000. 

No.  3  required  an  operating  cost  of  $75,000,  plus  a  total  tailing  and 
residue  loss  of  $39,000,  making  $114,000.  In  this  estimate,  as  in  No. 
2,  royalty  has  not  been  included  in  the  operating  cost. 

The  capital  cost  to  be  incurred  was  estimated  at  $52,000  for  No.  1, 
$42,000  for  No.- 2,  and  $50,000  for  No.  3  method. 

It  was  decided  that  the  saving  of  $15,000  per  annum  to  be  made 
by  consolidating  the  plant,  under  No.  1  method,  was  justified,  this 
decision  being  strengthened  by  the  disadvantage,  occurring  under 
No.  2  and  3  methods,  of  having  "to  choose  between  paying  a  royalty 
or  fighting  a  patent  suit. ' ' 

A  MEXICAN  MILL.  Next  I  shall  quote  figures  relating  to  a  silver 
mine  in  Mexico.  The  question  had  arisen  of  substituting  flotation  for 
cyanidation.  Experiments,  made  by  the  same  firm  as  had  tested  the 
North  Star  ore,  indicated  that  this  Mexican  ore  was  amenable  to  flota- 
tion. The  silver  sulphides  floated  readily;  the  recovery  ranged  from 
70  to  83%  of  the  combined  silver  and  gold,  varying  according  to  the 
proportion  of  oxidized  minerals  in  the  ore — oxidation  being  a  deterrent 
to  flotation,  of  course.  This  compares  with  an  extraction  of  91%  by 
the  existing  method,  which  gives  77%  of  the  metallic  content  as 
bullion  and  14%  as  concentrate.  But  a  closer  analysis  of  more  de- 
tailed data  is  required  to  make  a  trustworthy  comparison.  The  pres- 
ent method  of  treatment  includes  crushing  in  cyanide  solution  fol- 
lowed by  concentration  of  the  sand  on  Wilfley  tables  and  of  the  slime 
on  Deister  tables,  re-grinding  the  sand  and  cyaniding  an  all-slime 
product  The  capacity  of  the  plant  is  150,000  tons  per  annum  and  the 


FLOTATION    OF    GOLD    AND    SILVER  385 

ore  assays  $10.50  per  ton  when  silver  is  worth  65  cents  per  ounce. 
The  ratio  of  gold  to  silver  in  the  ore  is  10  oz.  silver  to  0.07  oz.  gold. 
The  tailing  is  worth  $1  per  ton.  The  total  cost  of  milling  is  $1.55  per 
ton,  to  which  must  be  added  10  cents  per  ounce  of  fine  metal  for 
marketing  the  bullion,  this  charge  including  export-tax,  expressage, 
and  refining,  and  15  cents  per  ounce  of  metal  for  marketing  the  con- 
centrate, this  expense  including  taxes,  freight,  smelting,  and  sacking. 
The  present  output  yields  a  bullion  700  fine  and  approximately  50 
tons  of  $350  concentrate  per  month. 

On  the  other  hand,  the  flotation  plant  would  cost  $50,000  and 
would  produce  100  to  150  tons  of  $500  to  $800  concentrate,  to  be 
marketed  at  a  cost  of  15c.  per  fine  ounce  and  leaving  a  tailing  assay- 
ing $2.10  per  ton.  The  Mexican  export-tax  on  concentrate  is  2%  (of 
gross  value)  more  than  on  bullion,  thus: 

Bullion,  %      Ore,% 

Federal    5  7 

State     2i  2i 

Total     7i  9i 

The  final  comparisons  are  as  follows: 

1.  Between     table-concentration     followed     by     cyaniding     and 
straight  flotation,  the  saving  in  cost  of  treatment  by  flotation  is  about 
equal  to  the  extra  recovery  by  tabling  and  cyaniding,  but  the  in- 
creased expense  for  marketing  the  large  tonnage  of  lower-grade  con- 
centrate plus  lower  smelter-returns  on  concentrate  than  on  bullion 
represents  a  loss  of  90  cents  per  ton  of  ore  by  straight  flotation. 

2.  Between  table-concentration  and  cyanidation,  as  against  flota- 
tion and  cyanidation  of  flotation  tailing,  the  extra  recovery  is  33  cents 
(extraction  94%)   and  the  saving  in  cost  is  57  cents  per  ton,  while 
the  additional  expense  of  marketing  the  concentrate  plus  lower  smelter- 
returns  on  concentrate  than  on  bullion  is  90  cents,  so  that  the  difference 
is  extinguished. 

Cyanide  is  taken  at  30  cents  per  pound,  1.8  to  2  Ib.  being  con- 
sumed per  ton  of  ore.  Lately  the  precarious  character  of  the  cyanide 
supply  has  furnished  an  argument  in  favor  of  flotation.  Packing  the 
concentrate  on  mule-back  or  freighting  it  by  train,  with  the  uncer- 
tainty of  getting  cars  for  shipment  to  a  smelter,  possibly  outside 
Mexico,  are  points  requiring  careful  consideration.  The  smelter  de- 
ductions are  important ;  usually  payment  is  made  on  95%  of  the  silver 
and  $19  (or  91.92%)  is  paid  per  ounce  of  gold  in  the  form  of  concen- 
trate against  100%  of  these  metals  in  the  form  of  bullion.  This 
represents  a  net  loss  of  6  to  8%  on  this  class  of  ore.  At  present  there- 
fore it  is  inadvisable  to  spend  $50,000  in  erecting  a  flotation  plant  to 


386  FLOTATION 

obtain  a  result  no  better  than  that  given  by  the  existing  system  of 
treatment,  but  it  may  prove  advantageous  in  the  future  to  adopt  nota- 
tion followed  by  cyanidation  when  the  flotation  product  itself  can  be 
treated  safely  and  profitably  on  the  spot,  yielding  bullion.  This  ex- 
ample will  serve  at  least  to  emphasize  the  fact  that  such  problems 
cannot  be  settled  in  the  laboratory,  and  to  show  that  the  object  of 
metallurgy  is  to  give  the  greatest  net  returns  rather  than  the  high- 
est percentage  of  extraction. 

THE  MELONES  MILL.  Another  interesting  comparison  between 
cyanidation  and  flotation  is  afforded  by  an  investigation  made  by  the 
Melones  Mining  Company,  which  treats  a  low-grade  gold  ore  typical 
of  this  part  of  the  Mother  Lode  region.  The  existing  plant  consists* 
of  100  stamps  weighing  1000  Ib.  each,  and  dropping  6  inches  at  the  rate 
of  107  drops  per  minute.  The  stamp-duty,  when  discharging  through 
a  20-mesh  screen,  is  5.3  tons.  No  plate-amalgamation  is  attempted  in- 
side the  mortar,  but  mercury  is  fed  into  the  battery,  and  the  pulp 
when  discharged  passes  over  the  usual  amalgamating  tables.  The  ore, 
a  gold-bearing  quartz  containing  pyrite,  averages  $3.65,  from  which 
$1.83,  or  50%,  is  extracted  by  amalgamation  and  cyanidation,  leaving 
a  51-cent  tailing  and  3.4%  of  concentrate  assaying  $36  per  ton.  The 
further  extraction  of  the  gold  in  the  concentrate  may  be  disregarded 
for  the  moment.  Of  the  total  extraction  43%  is  obtained  as  amalgam, 
17%  as  bullion  in  the  cyanide  annex,  and  40%  in  concentrate,  which 
also  is  treated  by  cyanidation.  The  pulp  from  60  stamps  passes  from 
the  amalgamating  tables  to  Wilfley  concentrators,  while  that  from  the 
new  mill  of  40  stamps  undergoes  classification  in  spitzkasten  before 
being  concentrated.  It  has  been  observed  in  the  Mother  Lode  region 
that  the  pulp  from  the  stamp-battery  does  not  concentrate  so  well 
after  hydraulic  classification  as  without  such  preliminary  treatment. 
Sizing  seems  to  be  preferable.  On  the  Wilfley  tables  the  gold-bearing 
pyrite  is  recovered  as  a  concentrate ;  at  the  same  time,  by  the  addition 
of  extra  water  in  the  feed-box  of  the  Wilfleys,  the  sand  and  slime  are 
separated  without  the  intervention  of  the  usual  de-sliming  classifiers. 
The  sand,  assaying  $1.15,  goes  to  the  leaching-vats  of  the  cyanide 
annex;  the  slime,  assaying  $1,  passes  through  cone-classifiers,  the 
underflow  from  which  joins  the  sand  in  the  leaching-vats,  while  the 
overflow  runs  to  the  slime-plant.  This  includes  Dorr  dewaterers  and 
Devereux  agitators,!  followed  by  Dorr  thickeners  and  an  Oliver  filter. 
A  middling,  assaying  $8  per  ton,  is  made  on  the  Wilfleys ;  this,  after 


*For  most  of  the  information  in  these  paragraphs  I  am  indebted  to  W.  G. 
Devereux,  manager  for  the  Melones  Mining  Company. 

fFor  a  description  of  these  machines  see  M.  &  S.  P.,  March  3,  1917. 


FLOTATION    OF    GOLD    AND    SILVER  387 

classification,  goes  to  six  'finishing'  Wilfley  tables,  the, tailing  from 
which  is  passed  to  the  sand-plant. 

The  following  facts  are  pertinent  to  our  enquiry.  The  Wilfley 
tables  recover  95%  of  the  gold  that  is  so  intimately  associated  with 
the  pyrite  as  to  have  escaped  amalgamation ;  such  gold-bearing  pyrite 
as  escapes  into  the  cyanide  annex  is  either  in  the  form  of  slime  or  it  is 
material  that  has  been  insufficiently  pulverized.  The  pulp  after  con- 
centration on  the  Wilfley  s  assays  $1.12,  whereas  the  mill-tailing,  dis- 
charged from  the  cyanide  annex,  assays  51c.  per  ton.  That  repre- 
sents the  residual  loss,  to  which  must  be  added  the  loss  in  the  treatment 
of  the  concentrate.  The  'sand'  and  'slime'  are  nearly  equal  in  weight. 
The  extraction  of  gold  from  the  'sand'  and  'slime'  together  is  about 
55%,  that  is,  55%  of  the  31%  of  gold  remaining  after  amalgamation 
and  concentration.  A  solution  containing  J  Ib.  KCN  per  ton  of  ore  is 
used  in  cyaniding  the  slime,  and  a  4-lb.  solution  on  the  sand.  The  total 
cost  of  milling  (excluding  concentration)  is  50  cents  per  ton  of  ore. 

What  can  flotation  do  on  this  ore?  Samples  were  sent  to  the  Min- 
erals Separation  people  in  San  Francisco  and  they  reported  thus: 

Weight  Gold  Recovery 

%  oz.  % 

Heading    100.0  0.06  100.0 

Concentrate     1.4  1.83  42.7 

Middling     6.2  0.20  20.7 

Tailing    92.4  0.02  30.8 

This  showed  a  recovery  of  63.4%,  including  the  middling,  which, 
in  mill-practice,  would  be  re-treated  continuously.  However,  account 
is  rendered  for  only  94.2%  of  the  total  gold  in  the  heading.  The 
material  tested  was  slime  from  the  Wilfley  tables,  the  screen-analysis 
showing  98%  through  200-mesh.  In  a  later  test,  made  at  the  same 
laboratory,  a  sample  of  the  pulp  as  it  came  from  the  amalgamating 
tables  was  subjected  to  flotation,  the  result  being  a  failure  owing  to 
the  coarseness  of  a  large  part  of  the  product.  After  the  sample  had 
been  re-ground,  until  only  4%  remained  on  a  200-mesh  screen,  the 

flotation  machine  did  as  follows : 

Weight  Gold  Recovery 

%                 oz.  % 

Heading    . 100.0  0.085  100.0 

Concentrate   1.7  4.400  88.4 

Tailing    98.3  0.010  11.6 

The  chief  engineer  (E.  H.  Nutter)  for  Minerals  Separation  re- 
ported that  this  test  "indicates  very  definitely  that  the  ore  as  sub- 
mitted can  be  given  flotation  treatment  usefully,"  but  it  must  be 
noted  that  the  sample  "as  submitted"  was  much  too  coarse  to  undergo 
successful  flotation.  The  extra  cost  of  re-grinding  to  200-mesh  is  a 


388  FLOTATION 

vital  factor  in  the  problem.  What  would  be  the  cost  of  re-grinding? 
At  a  neighboring  mine,  producing  a  similar  ore,  the  cost  of  re-grinding 
is  25c.  per  ton.  But  all  the  pulp  would  not  have  to  be  re-ground ;  only 
the  sand,  say,  275  tons  in  all,  out  of  the  daily 'output  of  530  tons. 
At  25c.  per  ton  on  275  tons,  the  cost  per  original  mill-feed  would  be 
12c.  per  ton  for  re-grinding. 

A  flotation  plant  to  treat  530  tons  of  such  ore  would  cost  $6000 
f .o.b.  San  Francisco,  or  $10,000  erected ;  but  the  necessary  re-grinding 
plant  would  cost  $20,000  more.  The  items  of  operating  cost  are  esti- 
mated, by  Mr.  Nutter,  as  follows,  per  ton  of  dry  ore : 

Cents 

Reagents    6 

Labor    5 

Power  (35  hp.  per  200-ton  unit) 2 

Royalty  at  25c.  per  oz.  gold . . : 2 

15 

To  this  must  be  added  the  present  cost  of  crushing  and  amalgama- 
tion, which  is  20c. ;  so  that  the  total  cost  of  combined  treatment,  to  the 
point  of  making  a  concentrate,  would  be 

Cents 

Crushing    20 

Re-grinding    12 

Flotation   15 

47 

This  compares  with  the  present  cost  of  50c.  Allowing  a  90% 
recovery  by  flotation,  as  against  the  present  86%,  on  a  $3.65  ore,  the 
additional  winning  would  be  14.6c.  per  ton. 

The  Melones  concentrate,  representing  3.4%  of  the  weight  of  ore, 
is  re-ground,  at  a  cost  of  50c.  per  ton,  to  pass  200-mesh  and  is  then 
cyanided,  without  roasting.  The  cost  of  treatment  is  $5.50  and  the 
extraction  is  92%.  The  cost  is  19c.  per  ton  of  crude  ore  and  the  tail- 
ing retains  9Jc.  in  gold. 

In  making  this  comparison  the  treatment  of  the  concentrate  is 
assumed  to  be  the  same,  whether  it  be  the  product  from  the  Wilfley 
tables  or  from  the  flotation-cells.  No  doubt  exists  as  to  the  successful 
treatment  of  the  flotation  concentrate,  which  would  not  require  re- 
grinding,  so  that  the  present  cost  of  re-grinding  the  concentrate, 
which  is  50c.  per  ton  of  concentrate,  or  1.5c.  per  ton  of  mill-feed, 
would  be  saved.  Moreover,  the  concentration  would  be  higher,  if  one 
may  judge  from  the  results  of  the  test  made  on  the  re-ground  pulp. 
In  that  experiment  the  concentrate  was  only  1.7%,  but  it  assayed  $88, 
that  is,  it  was  half  in  quantity  and  double  in  richness  as  compared  with 
the  Wilfley  product.  Apparently  the  re-grinding  had  liberated  some 


FLOTATION    OF    GOLD    AND    SILVER  389 

gold,  which  had  become  included  in  the  concentrate ;  on  the  other  hand, 
some  of  the  quartz  attached  to  pyrite  had  been  loosened  so  as  to  join 
the  rest  of  the  gangue  in  the  tailing.  The  reduction  in  the  weight  of 
concentrate  would  decrease  the  cost  of  treating  concentrate  from  19c. 
per  ton  to,  say,  15c.  The  higher-grade  concentrate  would  require 
more  careful  handling,  and  the  extraction,  at  the  same  ratio  of  92%, 
would  leave  a  higher  residue,  namely  8%  of  $88,  or  $7.04,  as.  com- 
pared with  8%  of  $36,  or  $2.88,  making  a  difference,  however,  of  only 
2c.  per  ton  of  original  ore,  owing  to  the  higher  rate  of  concentration 
by  flotation.  In  the  event  of  adapting  flotation  to  a  stamp-mill,  such 
as  that  of  the  Melones,  it  would  be  advisable  to  take  the  pulp  from 
the  amalgamating  tables  to  the  re-grinding  machinery,  in  preparation 
for  flotation,  and  not  to  attempt  any  table-concentration,  because 
flotation  would  be  better  when  leaving  the  pyrite  in  the  pulp  than 
when  treating  pulp  after  concentration.  It  only  remains  to  remark 
that  the  Melones  treatment  might  be  changed  to  all-sliming  and 
cyanidation,  discarding  concentration  and  separate  treatment  of  the 
concentrate,  f 

The  cost  might  be  reduced  3c.  per  ton,  but  it  must  be  remembered 
that  the  flotation  figure  is  only  an  estimate  as  against  the  actual  cost 
by  the  existing  method.  The  increased  extraction  might  be  15c.  per 
ton.  The  total  gain,  of  18c.  per  ton,  would  be  attractive  if  confirmed 
by  further  experiment,  and  if  the  use  of  flotation  did  not  involve 
inquisition  by,  and  subservience  to,  a  patent-exploiting  company. 
That  undoubtedly,  in  my  opinion,  is  a  deterrent  now.  If  it  were  a 
question  of  erecting  a  mill  on  a  mine  that  had  no  reduction  plant,  and 
that  produced  ore  of  the  kind  we  have  been  discussing,  it  would  be 
rational  to  adopt  flotation,  not  only  for  the  sake  of  the  small  extra 
extraction  but  on  account  of  the  first  cost  of  plant.  The  Melones 
cyanide  plant  cost  $50,000. 

THE  DUTCH-APP  MILL.  At  the  Dutch  and  App,  a  neighboring  group 
of  mines,  in  Tuolumne  county,  a  conventional  Californian  mill  of  40 
stamps  of  1050  Ib.  each,  followed  by  amalgamation  and  concentration, 
has  been  changed  from  concentration  by  Wilfley  tables  and  Frue 
vanners  to  flotation,  so  that  a  closer  comparison  is  possible.  I  am 
informed^  that  the  cost  in  the  old  mill  was  74  cents,  of  which  38c.  was 
for  stamping,  amalgamation,  and  concentration,  and  36c.  was  for  the 
transport  and  treatment  of  the  concentrate.  The  Californian  custom 


tCompare  this  with  the  Nickel  Plate  experience.  'The  Nickel  Plate  Mine 
and  Mill.'  By  T.  A.  Rickard.  M.  &  S.  P.,  January  20,  1917. 

JBy  W.  J.  Loring,  who,  I  hope,  at  a  later  date,  will  contribute  his  own 
testimony  on  the  subject. 


390  FLOTATION 

of  reporting  the  cost  of  milling  without  including  the  expense  of  realiz- 
ing upon  the  concentrate  is  misleading ;  so  also  is  the  practice  of  ignor- 
ing the  loss  or  smelter-deduction  from  the  assay-value  of  the  concen- 
trate. This  item  should  be  added  to  the  assay  of  the  mill-tailing  in 
order  to  ascertain  the  total  loss,  and  therefrom  the  total  extraction 
of  valuable  metal.  Thus  the  total  cost  in  the  old  mill  was  74c. ;  in  the 
modified  mill  it  was  found  to  range  between  88c.  and  $1  per  ton.  The 
modified  plant,  however,  is  at  best  a  mill  patched-up  for  the  purpose  of 
testing  the  ore  by  flotation ;  therefore,  the  cost  should  be  much  reduced. 
The  tonnage  treated  was  at  the  rate  of  200  tons  daily,  whereas  the 
proposed  new  mill  will  treat  600  tons  daily. 

The  tailing  in  the  old  mill,  treating  daily  200  tons  of  $3.75  ore, 
assayed  90  cents  (excluding  the  loss  in  concentrate-treatment),  but 
when  flotation  replaced  concentration  by  Wilfley  tables  and  Frue 
vanners  on  the  same  grade  of  ore,  the  tailing  was  reduced  to  35c. 
during  the  first  month  of  operation,  showing  a  saving  of  55c.  per  ton. 
The  comparative  cost  of  a  plant  to  treat  daily  200  tons  of  ore  carrying 
5%  of  concentratable  pyrite  is  estimated  under  normal  conditions 
as  follows : 

(1)  Twenty  stamps  of  1250  Ib.  each,  with  two  re-grinding  tube- 
mills,  plates,  and  vanners — including  rock-breaker,  $48,000. 

(2)  Same  mill,  using  flotation  in  place  of  vanners,  $55,000. 

(3)  Same  mill,  concentrating  on  tables,  the  sand  and  slime  treated 
by  cyanide,  $65,000. 

No.  3  does  not  include  the  treatment  of  concentrate,  because  it  is 
the  usual  custom  to  send  it  to  the  smelter  at  Selby.  It  will  be  noted 
that,  for  a  comparison  of  plant-cost,  No.  3  must  be  compared  with 
No.  2.  Flotation  has  given  a  slightly  higher  concentration  of  the 
gold-bearing  pyrite  in  the  Dutch- App  ore ;  thus : 

Old  mill,  4^%  of  $35  to  $40  concentrate. 

Flotation,  5%  of  $50  to  $65  concentrate. 

The  cost  of  transport  and  treatment  is  38c.  per  ton  of  ore.  The 
cost  of  haulage,  freight,  and  smelter  deductions  is  $9.50  per  ton  of 
concentrate.  The  cost  of  stamp-crushing  and  ball-mill  re-grinding 
together  is  35c.  per  ton.  The  cost  of  flotation  by  itself  is  15c.,  making 
88c.  per  ton  in  all  for  the  extraction  of  the  gold. 

When  the  new  mill  is  treating  500  to  600  tons  daily,  it  is  expected 
to  reduce  the  cost  to  68c.  and  the  tailing-loss  to  20c.  per  ton. 

By  way  of  further  comparison  I  may  quote  the  cost  of  milling  at 
an  up-to-date  plant,  using  stamps,  amalgamation,  and  table-concen- 
tration, namely,  at  the  Plymouth  Consolidated  in  Amador  county, 


FLOTATION    OP    GOLD   AND    SILVER  391 

also  on  the  Mother  Lode.  There  the  cost  of  milling  is  36c.  and  the 
concentrate  realization  24c.  more,  making  60c.  per  ton.  The  treatment 
is  most  satisfactory  because,  among  other  reasons,  the  yield  of  con- 
centrate is  only  1J%.  On  such  an  ore  flotation  would  not  be  as 
beneficial  as  on  the  Dutch- App  ore,  which  contains  5%  concentratable 
gold-bearing  pyrite. 

THE  ARGO  MILL.  A  tribute  to  the  elasticity  of  the  flotation  process 
is  furnished  by  the  use  of  it  in  a  plant  treating  custom  ores.  In  the 
Argo  mill,  at  Idaho  Springs,  Colorado,  it  has  been  found  highly  ad- 
vantageous to  substitute  flotation  for  cyanidation,  after  stamp-milling 
and  classification,  as  shown  on  the  accompanying  flow-sheet.*  Most 
of  the  ore  comes  through  the  Argo  (formerly  Newhouse)  adit,  which 
taps  the  veins  of  Clear  Creek  and  Gilpin  counties.  These  contain  gold 
and  silver  associated  with  pyrite,  chalcopyrite,  and  tetrahedrite,  so 
that  it  is  a  question  of  concentrating  the  sulphides  encasing  the 
precious  metals.  Much  of  the  ore  is  of  the  so-called  'free-milling' 
kind,  that  is,  it  is  amenable  to  stamp-mill  amalgamation.  The  coarse 
gold  is  caught  on  the  tables  before  flotation ;  the  fine  gold  is  caught  in 
the  flotation  concentrate.  Good  results  are  obtained  by  classifying 
before  flotation,  particularly  on  oxidized  ore.  A  trial  on  an  oxidized 
gold  ore  from  the  Paris  mine  yielded  86%  by  flotation  and  98%  by 
cyanidation.  The  mill  levies  the  same  charges  for  treatment  as  the 
smelter  at  Denver  and  has  helped,  by  its  competition,  to  lower  the 
smelter-rates.  Its  own  concentrate  is  sold  to  the  smelter.  Eens  E. 
Schirmer,  the  manager,  and  Jackson  Pearce,  the  metallurgist,  in- 
formed me  that  they  are  able  to  treat  ore  assaying  $40  to  $80  per  ton. 
They  quote  $10.50  for  treatment  on  a  $50,  and  over,  ore,  but  the  bulk 
of  the  custom  ores  that  come  to  this  mill  range  between  $9  and  $20, 
gross  value,  and  on  such  material  the  milling-charge  ranges  from  $4.75 
to  $5.50  per  ton. 

For  zinc  there  is  no  pay  and  also  no  penalty. 

For  lead  they  pay  the  regular  smelter  rate,  namely:  ''Deduct 
1.5%  from  wet  assay.  The  prices  paid  per  unit  for  lead  ore  are  based 
upon  a  quotation  of  $4  per  hundred  pounds,  Ic.  up  or  down  for  each 
change  of  5c.  in  this  quotation,  which  shall  be  90%  of  the  sales  prices 
in  New  York  of  the  A.  S.  &  R.  Co.  for  common  desilverized  lead, 
provided  said  price  does  not  exceed  $4  per  hundred  pounds.  When 
price  does  exceed  $4  per  hundred  pounds,  the  quotation  used  as  a 
basis  of  settlement  shall  be  $3.60  per  hundred  pounds,  plus  three- 


*See  also  an  excellent  article  by  Jackson  A.  Pearce.     'Flotation  Tribula- 
tions.   M.  &  S.  P.,  Sept.  16,  1916.    Re-printed  in  this  volume. 


392 


FLOTATION 

20  stamps  (1050  Ib.  each) 


Dorr  classifier 


Sand 
Card  tables 


Slime 
Dorr  thickener 


Concentrate 


Sand 
Tube-mill 


Slime-tables 


Concentrate 


Tailing 

I 

Dorr  thickener 


I 

Flotation  machine 


Flotation  machine 


Concentrate 


Tailing 


Concentrate 


Waste 

FLOW-SHEET   OF   ARGO    MILL 


fourths  the  excess  of  said  sales  price  above  $4  per  hundred  pounds. '  '* 
For  copper  they  pay  on  the  dry  assay,  that  is,   \%  deduction 


*I  quote  the  exact  words  in  order  that  the  reader  may  appreciate  the  hocus- 
pocus  of  this  smelter  method  of  fixing  the  price  of  lead.    It  is  to  laugh! 


FLOTATION   OF   GOLD   AND   SILVER  393 

from  the  wet  assay,  and  the  Western  Union  quotation  for  casting 
copper,  less  6c.  per  pound. 

For  silver,  they  deduct  \  oz.  from  assays  up  to  10  oz.  per  ton, 
and  pay  for  the  remainder  at  95%  of  New  York  quotation  on  date  of 
assay.  For  ore  over  10  oz.  per  ton,  they  pay  95%  of  the  quotation, 
without  further  deduction. 

For  gold  they  pay  $19  per  oz.  between  0.05  and  1.5  oz.  per  ton; 
on  richer  ore  they  pay  $19.50  per  ounce. 

The  Argo  mill,  with  its  flotation  annex,  has  treated  4  oz.  gold  ore, 
100  oz.  silver  ore,  40%  lead  ore,  and  5%  copper  ore  at  different  times. 
Such  high-grade  ore  is  mixed  with  the  lower-grade  before  being  milled. 
Money  has  been  made  even  on  a  $1.25  ore. 

It  was  found  that  the  recovery  by  flotation  was  slightly  better  than 
by  cyanidation;  moreover,  the  cost  was  lower,  owing  to  the  less  ex- 
pense in  chemicals.  A  much  simpler  flow-sheet  became  practicable; 
there  is  less  pumping,  less  power,  and  less  labor.  Hence  the  adoption 
of  flotation.  A  further  and  decisive  advantage  is  the  ability  to  bene- 
ficiate  the  base  metals,  notably  copper,  which  was  a  cyanicide.  Since 
flotation  was  introduced  the  mill  finds  a  wider  scope  and  is  able  to 
command  a  larger  custom.  The  flotation  machine  in  use  is  one  de- 
vised and  patented  by  Mr.  Pearce.  It  is  of  the  mechanical-agitation 
type,  but  it  consumes  less  than  one-third  of  the  power  required  by  the 
Minerals  Separation  machine  previously  used  in  this  mill.  A  6-cell 
Pearce  machine  requires  only  5.3  horse-power.  Two  such  6-cell  ma- 
chines are  employed,  one  to  treat  sand  (80%  -|-  200-mesh)  and  the 
other  to  treat  slime.  The  former  gives  the  higher  recovery.  I  watched 
them  at  work  and  can  testify  that  they  produced  a  uniformly  good 
froth  and  appeared  to  be  operating  admirably.  Two  pounds  of  an 
oil-mixture,  consisting  of  two  parts  of  gas-oil  to  one  part  of  pine-oil 
(Pensacola  Tar  &  Turp.  Co/s  No.  400),  is  used  per  ton  of  ore.  The 
gas-oil  comes  from  Wyoming ;  it  is  one  from  which  the  lighter  gasoline 
has  been  removed.  The  more  sulphidic  an  ore  the  larger  the  propor- 
tion of  oil  required.  As  soon  as  sulphide  particles  appear  in  the  tail- 
ing, more  oil  is  added.  Gas-oil  costs  6c.  per  gal.  and  pine-oil  32c. 
laid  down.  The  water  is  neither  acid  nor  alkaline.  Neither  acid  nor 
alkali  is  added.  Fresh  water  is  used,  there  being  no  return  of  water 
from  the  tailing.  By  using  fresh  water  the  millman  avoids  fouling 
of  the  liquid  by  an  accumulation  of  colloids.  Formerly  the  overflow 
from  the  concentrate-thickener  was  run  back  to  the  flotation-cell 
but  it  was  found  that  this  closed  circuit  tended  to  collect  colloids 
detrimental  to  a  high  recovery  by  flotation. 

Experiments  have  been  made  with  as  much  as  40  Ib.  oil  per  ton  of 


394  FLOTATION 

ore ;  the  recovery  was  slightly  higher  than  when  using  2  Ib.  per  ton. 
What  a  commentary  on  the  'critical'  point!  When  using  40  Ib.  of  oil 
the  bubbles  are  smaller  owing  to  the  larger  proportion  of  gas-oil, 
which  was  increased  to  85%  of  the  oil-mixture.  When  using  5  to  6 
Ib.  oil  and  storing  the  concentrate  in  a  wooden  bin,  Mr.  Pearce  noticed 
that  the  oil  seeped  visibly. 

Ordinary  variations  of  temperature  appear  to  have  no  effect.  In 
winter  the  froth  freezes  occasionally,  so  that 'it  sinks,  but  so  long  as  the 
temperature  is  just  short  of  freezing  the  operation  is  not  affected. 
In  summer  the  recovery  is  no  higher  than  in  winter.  The  mill  recovers 
92%  of  the  gross  market-value  of  the  various  ores  and  treats  100 
tons  daily. 

THE  PORTLAND  MILL.  As  yet  scarcely  anybody  that  has  tried  nota- 
tion has  discarded  it  after  trial.  One  example  of  such  a  reversal  is 
furnished  by  the  Portland  Gold  Mining  Co.  of  Cripple  Creek,  and  the 
reasons  for  it  are  interesting. 

The  ore  was  dump  material  assaying  $2.25  per  ton,  carrying  half 
an  ounce  of  silver  for  every  ounce  of  gold,  both  minerals  being  present 
as  tellurides,  chiefly  calaverite.  After  treating  over  100,000  tons  the 
management  decided  that  flotation  was  not  superior  to  their  older 
method  of  treatment  by  table-concentration  and  cyanidation,  for  the 
following  reasons : 

(1)  Good  extractions  are  obtained  by  cyanidation  when  grinding 
to  20-mesh,  whereas  flotation  calls  for  grinding  to  48-mesh.     This 
extra  work  costs  lOc.  per  ton,  which  is  a  serious  item  on  $2.25  ore. 

(2)  Cyanide  bullion  is  sold  to  the  Mint,  and  the  small  amount  of 
concentrate  that  is  made  is  so  low  in  silica  and  so  high  in  iron  that  it 
can  be  marketed  at  the  smelter  on  easy  terms,  whereas  flotation  yields 
a  large  amount  of  silicious  concentrate  on  which  the  cost  of  freight  and 
treatment  is  three  times  that  of  marketing  the  by-product  of  a  cyanida- 
tion mill.     On  this  ore  the  recovery  by  flotation  was  found  to  be  in- 
versely proportional  to  the  grade  of  the  concentrate ;  a  high  recovery 
made  a  large  amount  of  low-grade  concentrate;  a  small  amount  of 
high-grade  concentrate  entailed  a  poor  recovery. 

(3)  Only  $20  per  ounce  was  paid  for  gold  in  the  flotation  con- 
centrate, and  nothing  for  the  silver.     Cyanide  bullion  is  sold  to  the 
Mint  at  $20.67  per  ounce  for  gold  and  95%  of  New  York  quotation 
for  silver.    Thus  4%  more  is  received  for  the  product  from  the  table- 
concentrate  than  for  the  flotation  product.     On  account  of  the  highly 
silicious  character  of  the  latter  it  was  found  that  the  cost  of  marketing 
at  tb/a  smelter  was  out  of  all  reason,  whereupon  it  was  sent  to  the 


FLOTATION    OF    GOLD    AND    SILVER  395 

custom  roasting-cyaiiide  mills  at  Colorado  Springs.  This  flotation 
concentrate  proved  ideal  stuff  to  treat  after  roasting,  but  as  the  silver 
is  not  recoverable  after  the  ore  has  been  roasted,  the  mill  could  not 
pay  for  it. 

(4)     The  royalty  payable  to  the  Minerals  Separation  company. 

The  principal  difficulty  was  to  make  a  high-grade  concentrate  and 
a  low-tailing  concurrently.  Amorphous  slime  rises  with  the  froth, 
and  any  effort  to  prevent  it  involves  a  loss  of  the  sulpho-telluride 
mineral ;  in  short,  it  is  difficult  to  separate  the  gangue-slime  from  the 
mineral  in  this  particular  ore.  Any  free  gold  in  the  ore  floats  with 
the  telluride  and  sulphide  minerals.  Incidentally,  it  is  worthy  of  note 
that  flotation  in  cyanide  solution  was  accomplished  successfully  at  the 
Portland  by  J.  M.  Tippett.  He  had  to  use  caustic  soda,  in  preference 
to  lime,  in  order  to  ensure  sufficient  alkalinity.  The  ore  was  ground 
in  the  presence  of  caustic  soda  and  cyanide.  Mr.  Tippett  avoided  de- 
watering,  and  the  consequent  loss  of  cyanide,  by  establishing  a  closed 
circuit.  The  pulp  flowed  from  the  flotation-cells  to  thickeners  and 
pachucas,  and  thence  to  niters.  By  this  method  of  treatment  he  was 
able  to  obtain  a  40c.  tailing  on  a  $20  ore.  From  $17  to  $18  was  taken 
off  in  the  form  of  a  12-ounce  flotation  concentrate,  the  tailing  from 
which  assayed  $2  or  $3  per  ton  and  was  reduced  to  40c.  by  treatment 
in  a  pachuca. 

SUMMARY.  In  most  cases  the  substitution  of  flotation  means  the 
making  of  a  concentrate  instead  of  bullion.  The  latter  is  ready  for 
the  market  and  easily  handled  or  transported.  The  concentrate  is 
bulky  and  if  it  has  to  be  shipped  elsewhere  for  treatment  the  handling 
of  it  entails  loss,  to  which  must  be  added  freight  and  smelter  deduc- 
tions. However,  these  are  troubles  that  can  be  obviated  if  the  concen- 
trate is  treated  at  the  mine.  Some  difficulty  is  said  to  have  been 
caused  by  the  oil  retained  by  the  concentrate;  it  may  interfere  with 
cyairidation,  as  Paul  W.  Avery  testifies,*  but  we  have  the  statement  of 
E.  M.  Hamilton!  that  he  has  treated  several  samples  of  flotation 
concentrate  with  complete  success.  The  experience  at  the  Melones 
mine  is  to  the  point.  Speaking  generally,  I  infer  that  if  an  ore  can  be 
cyanided,  then  its  concentrate,  obtained  by  flotation,  can  also  be 
cyanided  successfully.  In  short,  any  gold  and  silver  ore  that  can  be 
amalgamated  or  cyanided  is  amenable  to  flotation,  and  the  resulting 
concentrate  is  equally  amenable  to  treatment  by  cyanidation.  In  some 
cases,  as  with  Cripple  Creek  tellurides  and  the  Cobalt  silver  minerals, 


*'Cyanidation  of  Flotation  Concentrate.'    M.  &  S.  P.,  May  16,  1916. 
tM.  &  S.  P.,  March  11,  1916. 


396  FLOTATION 

it  may  be  necessary  to  roast  first,  but  the  use  of  flotation  on  precious- 
metal  ores  need  not  involve  dependence  upon  a  smelter.  That  is  im- 
portant. On  the  concentrate  made  at  Cobalt,  for  example,  the  total 
cost  of  marketing  is  $38  per  ton.  A  chloridizing  roast  followed  by 
leaching  appears  to  be  the  only  escape  from  this  exaction.  In  Cali- 
fornia, the  marketing  of  concentrate  from  a  Mother  Lode  mine  in- 
volves a  cost,  in  freight,  treatment,  and  other  deductions  at  the 
smelter,  of  $9  to  $15  per  ton.  This  can  be  avoided,  at  many  mines, 
by  cyanidation  on  the  spot  without  roasting,  at  a  cost  of  about  $5 
per  ton. 

Thus  we  see  that  the  substitution  of  flotation  for  the  older  proc- 
esses of  amalgamation  and  cyanidation  is  an  economic  rather  than  a 
metallurgic  problem.  In  most  of  the  specific  cases  discussed  in  detail 
it  is  safe  to  assume  that  if  the  manager  were  starting  today  to  equip 
his  mine  with  a  mill,  he  would  select  the  flotation  process  rather  than 
the  older  methods,  or  make  flotation  a  part  of  his  flow-sheet.  The  scrap- 
ping of  an  existing,  and  expensive,  plant  is  quite  another  matter. 
Usually  the  simple  flotation  plant  would  cost  half  that  of  the  more 
complicated  cyanide  annex.  Yet,  in  conversation  with  various  man- 
agers, I  have  ascertained  that  the  control  or  assumed  control  of  the 
basic  flotation  patents  by  the  Minerals  Separation  people  is  a  strong 
deterrent.  Most  of  us  do  not  like  to  be  inquisitioned  by  the  agents  of 
a  patent-exploiting  company,  nor  do  technical  men  care  to  be  placed 
under  pledges  of  professional  secrecy  to  anybody.  The  royalty  on 
gold  is  only  25  cents  per  ounce  and  on  silver  2J%,  so  that  the  tax  is 
not  onerous,  but  a  tax  of  any  kind  is  an  irritation  to  most  men,  par- 
ticularly when  the  right  of  the  tax-gatherer  is  still  undecided  by  the 
courts  of  law.  If  .and  when  this  question  of  Minerals  Separation's 
right  to  collect  a  royalty  is  decided  satisfactorily  we  may  expect  a 
wide  extension  in  the  application  of  flotation  to  ores  chiefly  valuable 
for  gold  and  silver. 


FLOTATION    LITIGATION  397 

FLOTATION  LITIGATION 

BY  T.  A.  RICKARD 
(From  the  Mining  and  Scientific  Press  of  April  14,  1917) 

The  story  of  American  litigation  over  the  flotation  patents  is  inter- 
esting and  perplexing.  The  first  contest  over  the  validity  of  the  Min- 
erals Separation  company 's  principal  patent  was  caused  by  James  M. 
Hyde,  who,  in  August  1911,  introduced  the  use  of  froth-flotation  at  the 
mill  of  the  Butte  &  Superior  Copper  Company,1  applying  the  process 
successfully  to  a  zinc  ore  carrying  a  small  amount  of  lead.  On  October 
3,  1911,  suit  for  infringement  of  patent  835,120  was  brought  by  Min- 
erals Separation  against  Mr.  Hyde.  The  trial  took  place  before  the  U. 
S.  District  Court  at  Butte  and  there,  on  July  28,  1913,  Judge  Bour- 
quin  decided  that  the  patent  was  valid  "in  respect  to  all  claims  in 
issue. ' ' 

It  will  be  well  to  outline  the  nature  of  the  patent  in  suit.  The  first 
claim  says:  "The  herein-described  process  of  concentrating  ores  which 
consists  in  mixing  the  powdered  ore  with  water,  adding  a  small  propor- 
tion of  any  oily  liquid  having  a  preferential  affinity  for  metalliferous 
matter  (amounting  to  a  fraction  of  one  per  cent  on  the  ore),  agitating 
the  mixture  until  the  oil-coated  mineral  matter  forms  into  a  froth,  and 
separating  the  froth  from  the  remainder  by  flotation." 

Claim  No.  12  states:  "The  process  of  concentrating  powdered  ore 
which  consists  in  separating  the  minerals  from  gangue  by  coating  the 
minerals  with  oil  in  water  containing  a  fraction  of  one  per  cent  of  oil 
on  the  ore,  agitating  the  mixture  to  cause  the  oil-coated  mineral  to 
form  a  froth,  and  separating  the  froth  from  the  remainder  of  the 
mixture. ' ' 

The  patentees — H.  L.  Sulman,  H.  F.  K.  Picard,  and  John  Ballot 
—refer  in  their  specification  to  the  Cattermole  patent.  No.  777,273,  in 
which  mention  is  made  of  using  ' '  an  amount  of  oil  varying  from  four 
per  cent  to  six  per  cent  of  the  weight  of  metalliferous  matter  present," 
and  they  then  proceed  to  explain : 

"We  have  found  that  if  the  proportion  of  oily  substance  be  con- 
siderably reduced — say,  to  a  fraction  of  one  per  cent  on  the  ore — gran- 
ulation ceases  to  take  place,  and  after  vigorous  agitation  there  is  a  tend- 


iThis  company  did  not  produce  copper,  but  zinc,  lead,  and  silver.     In  1916 
the  name  was  changed  to  Butte  &  Superior  Mining  Company. 


398  FLOTATION 

ency  for  a  part  of  the  oil-coated  metalliferous  matter  to  rise  to  the  sur- 
face of  the  pulp  in  the  form  of  a  froth  or  scum.  This  tendency  is  de- 
pendent on  a  number  of  factors.  Thus  the  water  in  which  the  oiling  is 
effected  is  preferably  slightly  acidified  by  adding,  say,  a  fraction  of  one 
per  cent  up  to  one  per  cent  of  sulphuric  acid  or  other  mineral  acid  or 
acid  salt ;  the  effect  of  this  acidity  being  to  prevent  gangue  from  being 
coated  with  oily  substance,  or,  in  other  words,  to  render  the  selective 
action  of  the  oil  more  marked ;  but  it  is  to  be  understood  that  the  ob- 
ject of  using  acid  in  the  pulp  according  to  this  'invention  is  not  to 
bring  about  the  generation  of  gas  for  the  purpose  of  notation  thereby, 
and  the  proportion  of  acid  is  insufficient  to  cause  chemical  action  on  the 
metalliferous  minerals  present.  Again,  we  have  discovered  that  the 
tendency  for  the  oily  substance  to  disseminate  through  the  pulp  and 
the  rapidity  with  which  the  metalliferous  matter  becomes  coated  is  in- 
creased if  the  pulp  is  warmed.  The  formation  of  froth  is  assisted  by 
the  fine  pulverization  of  the  ore,  and  we  find  that  slime  mineral  most 
readily  generates  scum  and  rises  to  the  surface,  while  larger  particles 
have  less  tendency  to  be  included  in  the  froth." 

Application  for  this  patent  was  filed  on  May  29,  1905,  and  the 
rights  accruing  under  the  patent  start  from  this  date.  The  patent  was 
granted  on  November  6,  1906,  and  the  life  of  the  patent,  17  years,  is 
measured  from  this  later  date. 

Judge  Bourquin's  decision  was  sweeping.2  It  rested  largely  on  a 
reply  to  the  question  whether  Froment's  British  patent  No.  12,778,  of 
June  4,  1902,  anticipated  the  patent  in  suit.  On  this  point  the  Court 
expressed  itself  as  follows : 

"Froment's  [patent]  requires  several  times  the  quantity  of  oil  that 
does  this  in  suit,  both  by  examination  of  the  patents  and  working  de- 
scription and  by  tests  in  evidence.  Froment  crushes  the  ore  in  two  op- 
erations, and  de-slimes  it  before  treatment,  because  the  slime  is  too  fine 
to  be  treated  by  his  process,  while  the  process  in  suit  needs  but  one 
crushing  operation,  and  finds  slime  advantageous  and  most  easily  re- 
covered. Froment  employs  carbonate  of  lime;  the  process  in  suit  does 
not.  Froment  requires  acid,  and  in  greater  quantity  and  for  a  differ- 
ent function  than  does  the  process  in  suit,  which  latter  may  or  may  not 
use  acid.  Both  may  use  heat,  and  both  require  agitation — Froment's 
agitation  only  to  disseminate  the  oil,  the  process  in  suit  for  that  pur- 
pose and  also  to  aerate.  Froment's  result  is  by  flotation  by  gas  gener- 
ated in  situ ;  this  in  suit  is  by  flotation  by  air  introduced  by  vigorous 
agitation.  Froment's  product  is  like  unto  a  magma,  a  spongy,  pasty 


2For  full  text  of  this  decision  see  M.  &  S.  P.^August  16,  1913. 


FLOTATION    LITIGATION  399 

mass  of  oil  and  metallic  particles,  and  more  or  less  gas  bubbles,  while 
this  in  suit  is  a  froth  of  oil  and  metallic  particles  and  air-bubbles.  Fro- 
ment's  requires  oil  in  such  quantity  that  he  deems  it  worthy  of  recov- 
ery from  the  concentrate,  so  far  as  it  can  be ;  this  in  suit  so  little  oil  it 
disappears,  is  not  sensible  to  sight  or  touch  upon  the  concentrate  but 
only  to  analysis.  In  Froment's  it  would  seem  that  the  metallic  parti- 
cles are  floated  like  the  basket  of  a  balloon,  while  in  this  like  the  very 
envelope  of  a  balloon.  Froment's  is  costly,  while  this  is  cheap.  And 
from  the  evidence  it  would  seem  that  Froment's  process  would  fail  in 
practical  operation,  while  this  in  suit  has  succeeded.  In  Froment's  he 
oils  the  metallic  particles  by  agitation ;  then,  when  the  mixture  is  qui- 
escent, generates  gas  therein  by  quick  reaction,  followed  by  immediate 
and  direct  rising  of  the  gas  bubbles  to  the  surface  in  which  they  may 
come  into  contact  with  but  few  metallic  particles.  In  this  in  suit  vigor- 
ous agitation  of  the  mixture  beats  great  and  excess  volumes  of  air 
therein,  likely  bringing  the  ultimate  air  bubbles  into  repeated  contact 
with  many  metallic  particles.  The  action  of  the  gas  in  Froment  's  is  al- 
most explosive  in  nature.  He  speaks  of  the  proportion  of  carbonate  of 
lime  to  be  sought  as,  in  his  test-tube  example,  the  reaction  may  be  so 
sudden  and  violent  as  to  project  the  metallic  particles  out  of  the  tube. 
Froment's  gas  bubbles,  quick  formed  and  quick  rising  it  may  be,  arrive 
at  the  surface  with  expansion  still  in  progress.  These  or  analogous  rea- 
sons may  account  for  Froment's  magma  breaking  gas  bubbles  and  frag- 
ile evanescent  froth  in  so  far  as  his  result  is  like  unto  froth,  and  also 
may  account  for  the  process  in  suit's  strong  and  lasting  froth.'5 

On  appeal  to  the  Ninth  Circuit  in  San  Francisco  the  decision  of  the 
lower  court  was  reversed,  on  May  4,  1914.  The  opinion  of  the  Court  of 
Appeals,  pronounced  by  Judge  Gilbert,  stated  that  ''the  fact  that  the 
appellees  use  a  smaller  quantity  of  oil  than  was  used  in  the  prior  art  is 
not  of  itself,  and  is  not  claimed  by  them  to  be,  sufficient  to  distinguish 
their  process  so  as  to  render  it  patentable. ' '  This  Court  held  that ' '  the 
agitating  of  the  mixture  to  cause  the  oily-coated  mineral  to  form  a 
froth"  was  "clearly  anticipated  by  the  prior  art."  It  is  noteworthy 
that  the  Examiner  of  Patents  rejected  claim  No.  12  "in  view  of  763,- 
260,  Cattermole,  June  21,  1904;  or  793,808,  Sulman  et  al,  July  4,  1905, 
...  as  expressing  merely  a  difference  of  degree  thereover  as  to  the 
proportion  of  oily  matter  employed."  Thus  the  Examiner  refused  to 
allow  patentability  on  the  mere  use  of  a  small  percentage  of  oil.  The 
claim  thus  cancelled,  not  the  No.  12  of  the  final  patent,  quoted  above, 
was  the  only  one  that  was  based  exclusively  on  the  use  of  a  fraction  of 
1%  of  oil,  without  reference  to  a  particular  kind  of  agitation  or  a  par- 


400  FLOTATION 

ticular  kind  of  froth.  The  Appellate  Court  took  cognizance  of  this 
interesting  disclosure,  for  Judge  Gilbert  said.3 

"We  hold  that  to  sustain  the  appellees'  patent  would  be  to  give  to 
the  owners  thereof  a  monopoly  of  that  which  others  had  discovered. 
What  they  claim  to  be  the  new  and  useful  feature  of  their  invention,  as 
stated  by  their  counsel,  is  'agitating  the  mixture  to  cause  the  oily-coated 
mineral  to  form  a  froth. '  As  we  have  seen,  that  feature  was  clearly  an- 
ticipated by  the  prior  art,  and  when  the  elements  of  the  appellees' 
claims  are  read  one  by  one  it  will  be  found  that  each  step  in  their  proc- 
ess is  fully  described  in  more  than  one  of  the  patents  of  the  prior  art, 
with  the  single  exception  of  the  reduced  quantity  of  oil  which  they  use. 
The  patentees  of  the  appellees'  patent  made  a  valuable  contribution  to 
the  art  in  discovering  the  smallest  quantity  of  oil  which  would  produce 
the  desired  result.  In  doing  so  they  pursued  the  course  which  all  skil- 
ful metallurgists  would  be  expected  to  pursue.  They  made  a  series  of 
experiments  to  determine  how  small  a  quantity  of  oil  could  be  used 
successfully.  They  found,  as  all  must  find  who  apply  the  oil  flotation 
process,  that  certain  oils  are  adapted  to  use  with  certain  ores,  and  that 
a  larger  quantity  of  oil  is  necessary  for  one  kind  of  ore  than  for  an- 
other. The  appellees  admit  that  for  some  ores  they  use  four  times  as 
much  oil  as  for  others.  Their  discovery  that  a  small  fraction  of  one 
per  cent  of  oil  is  sufficient  to  produce  flotation  of  the  metalliferous  mat- 
ter cannot,  as  we  have  seen,  be  made  by  itself  or  in  a  combination  the 
subject  of  a  patent.  The  appellees  cannot  take  from  others  the  right 
to  use  oil  economically.  This  was  evidently  the  ruling  of  the  Patent 
Office  on  their  application  for  a  patent.  One  of  their  claims  in  the  orig- 
inal application  was  'the  process  of  concentrating  powdered  ore, 
which  consists  in  separating  minerals  from  gangue  by  coating  the  min- 
erals with  oil  in  water  containing  a  fraction  of  one  per  cent  of  oil  on 
the  ore,  and  recovering  the  oil-coated  minerals. '  This  was  rejected  in 
view  of  the  Cattermole  patent  '  as  expressing  merely  a  difference  of  de- 
gree thereover  as  to  the  proportion  of  oily  matter  employed. '  Counsel 
for  appellees  admit  that  the  claim  was  properly  rejected  for  the  reason 
that  it  leaves  out  the  agitation  and  froth,  and  say  'our  invention  is 
something  else  than  the  mere  reduction  of  oil. '  ' 

Thereupon  Minerals  Separation  obtained  a  hearing  before  the  Su- 
preme Court  of  the  United  States  on  a  writ  of  certiorari.  The  case 
was  argued  in  October  1916.  The  court  expressed  its  opinion  through 
Mr.  Justice  Clark  on  December  11,  1916.  It  was  laid  down  that  the 
patent  was  valid  on  three  counts,  (1)  the  use  of  a  ' critical'  and  minute 


•Tor  the  full  text  of  this  decision  see  M.  &  S.  P.,  May  9,  1914. 


FLOTATION    LITIGATION  401 

proportion  of  oil,  (2)  the  use  of  a  particular  kind  of  agitation,  namely 
"by  beating  air  into  the  mass,"  and  (3)  the  production  of  a  "peculi- 
arly coherent  and  persistent"  kind  of  froth.  The  most  important 
parts  of  the  opinion  are  to  be  found  in  three  paragraphs.4  The  first 
defines  the  patent : 

1 '  The  process  of  the  patent  in  suit,  as  described  and  practised,  con- 
sists in  the  use  of  an  amount  of  oil  which  is  'critical,'  and  minute  as 
compared  with  the  amount  used  in  prior  processes  'amounting  to  a 
fraction  of  one  per  cent  on  the  ore, '  and  in  so  impregnating  with  air  the 
mass  of  ore  and  water  used,  by  agitation — 'by  beating  air  into  the 
mass' — as  to  cause  to  rise  to  the  surface  of  the  mass,  or  pulp,  a  froth, 
peculiarly  coherent  and  persistent  in  character,  which  is  composed  of 
air  bubbles  with  only  a  trace  of  oil  in  them,  which  carry  in  mechanical 
suspension  a  very  high  percentage  of  the  metal  and  metalliferous  par- 
ticles of  ore  which  were  contained  in  the  mass  of  crushed  ore  subjected 
to  treatment.  This  froth  can  be  removed  and  the  metal  recovered  by 
processes  with  which  the  patent  is  not  concerned/' 

"It  is  obvious  that  the  process  of  the  patent  in  suit,  as  we  have  de- 
scribed it,  is  not  of  the  Metal  Sinking  class,  and  while  it  may,  in  terms, 
be  described  as  a  Surface  Flotation  process,  yet  it  differs  so  essentially 
from  all  prior  processes  in  its  character,  in  its  simplicity  of  operation, 
and  in  the  resulting  concentration,  that  we  are  persuaded  that  it  con- 
stitutes a  new  and  patentable  discovery. ' ' 

The  third  declares  the  Validity  of  the  patent,  but  restricts  its  ap- 
plication. 

"While  we  thus  find  in  favor  of  the  validity  of  the  patent,  we  can- 
not agree  with  the  District  Court  in  regarding  it  valid  as  to  all  of  the 
claims  in  suit.  As  we  have  pointed  out  in  this  opinion  there  were  many 
investigators  at  work  in  this  field  to  which  the  process  in  suit  relates 
when  the  patentees  came  into  it,  and  it  was  while  engaged  in  study  of 
prior  kindred  processes  that  their  discovery  was  made.  While  the  evi- 
dence in  the  case  makes  it  clear  that  they  discovered  the  final  step 
which  converted  experiment  into  solution,  'turned  failure  into  success' 
(The  Barbed  Wire  Patent,  143  U.  S.  275,)  yet  the  investigations  pre- 
ceding were  so  informing  that  this  final  step  was  not  a  long  one  and  the 
patent  must  be  confined  to  the  results  obtained  by  the  use  of  oil  with- 
in the  proportions  often  described  in  the  testimony  and  in  the  claims  of 
the  patents  as  'critical  proportions'  'amounting  to  a  fraction  of  one  per 
cent  on  the  ore, '  and  therefore  the  decree  of  this  court  will  be  that  the 


full  text  see  M.  &  S.  P.,  December  30,  1916. 


402  FLOTATION 

patent  is  valid  as  to  claims  No.  1,  2,  3,  5,  6,  7,  and  12,  and  that  the  de- 
fendant infringed  these  claims,  but  that  it  is  invalid  as  to  claims  9,  10, 
and  11.  Claims  No.  4,  8,  and  13  were  not  considered  in  the  decree  of 
the  two  lower  courts  and  are  not  in  issue  in  this  proceeding." 

Meanwhile  a  number  of  Western  mining  companies  had  begun  to 
use  flotation.  One  of  them  was  the  Miami  Copper  Company,  in  Ari- 
zona. On  October  10,  1914,  suit  was  brought  by  Minerals  Separation 
for  infringement  of  patent  No.  835,120  and  also  of  No.  962,678  and 
1,099,699.  The  first  trial  took  place  in  the  District  Court  at  Wil- 
mington, Delaware,  and  the  decision,  by  Judge  Bradford,  was  pro- 
nounced on  September  30,  1916. 5 

In  this  case  the  issue  differed  from  that  involved  in  the  previous 
litigation.  Hyde  had  denied,  not  infringement,  but  the  validity  of  pat- 
ent 835,120.  The  Miami  company  denied  infringement,  claiming  that 
it  was  using  a  method  similar  to  that  described  in  a  patent  of  earlier 
date,  namely  No.  793,808.  Judge  Bradford  accepted  this  contention. 
He  said : 

"The  evidence  shows  that  the  defendant  in  its  concentration  of  ore 
in  its  pneumatic  flotation  plant  employs  the  process  of  patent  No.  793,- 
808,  of  July  4,  1905,  to  Sulman  &  Picard,  hereinbefore  discussed,  as 
modified  by  the  use  of  certain  apparatus,  substantially  the  same  as  a 
portion  of  the  apparatus,  the  operation  of  which  is  described  in  the 
above-mentioned  Callow  patent,"  namely,  No.  1,104,755  of  July  21, 
1914,  to  John  M.  Callow. 

He  decided  that  the  Froment  patent  was  not  an  anticipation  be- 
cause "it  does  not  appear  that  there  was  present  in  the  Froment 
process  the  very  minute  quantity  of  oil  of  the  first  patent  in  suit. ' ' 

The  essential  part  of  the  Wilmington  decision  is  that  the  diminution 
of  oil  to  less  than  1%  of  the  weight  of  the  ore  is  patentable.  Judge 
Bradford  said: 

"On  the  whole  I  am  satisfied  that  the  first  patent  in  suit  must  be 
sustained  as  to  claims  1  and  12,  but  not  as  to  claim  9.  The  two  former 
are  definite,  specifiying  and  limiting  the  amount  of  oil  to  be  used;  claim 
1  mentioning  '  a  small  proportion  *  *  *  amounting  to  a  fraction  of  one 
per  cent  on  the  ore, '  and  claim  12  '  a  fraction  of  one  per  cent  of  oil  on 
the  ore.'  Claim  9  mentions  *  a  small  quantity  of  oil. '  This  is  so  indef- 
inite as  to  render  the  claim  void,  unless  on  consideration  of  the  patent 
as  a  whole  the  claim  can  by  construction  be  limited  to  the  use  of  oil 
amounting  to  only  a  fraction  of  one  per  cent.  The  patentability  of  the 
process  of  the  first  patent  in  suit  resides  in  the  use  of  oil  in  the  ex- 


full  text  of  this  decision  see  M.  &  S.  P.,  October  14  and  21,  1916. 


FLOTATION    LITIGATION  403 

tremely  minute  proportion  disclosed  in  the  descriptive  portion  of  the 
patent  to  effect  separation  of  froth  with  its  metallic  particles  from  the 
remainder  of  the  mixture  by  notation.  The  amount  there  disclosed  is 
not  in  excess  of  '  a  fraction  of  one  per  cent  on  the  ore '  and  may  be  only 
one-tenth  of  one  per  cent  on  the  ore,  or  even  less.  If,  then,  by  construc- 
tion claim  9  should  be  so  limited  as  to  be  restricted  to  the  use  of  oil 
amounting  to  only  a  fraction  of  one  per  cent  on  the  ore,  that  claim  is 
in  substance,  though  not  in  exact  phraseology,  the  same  as  claim  1  for 
the  reason  that  in  any  event  from  the  nature  of  the  invention  it  would 
be  necessary  to  read  'by  flotation'  into  claim  9,  if  in  other  respects 
valid.  But  a  limitation  by  construction  producing  such  a  result  is  in- 
admissible. It  is  suggested  by  one  of  the  plaintiff's  counsel  in  his  con- 
sideration of  claim  9,  that  one  for  the  purpose  of  securing  immunity 
from  the  consequences  of  infringement  might  use  an  oil  useful  in  the 
process,  and  add  to  it  an  oil  not  useful  as  applied  to  his  particular  ore, 
and,  on  being  sued  for  infringement  contend,  'I  am  using  1.1%  of  oil. 
I  do  not  infringe.  I  am  using  more  than  a  fraction  of  1%  of  oil. '  But 
the  existence  of  this  possibility  does  not,  I  think,  warrant  such  a  con- 
struction of  claim  9  as  is  urged ;  for  the  disclosure  of  the  patent  does 
not  extend  to  the  use  of  1.1%  of  oil,  but  is  limited  to  a  fraction  of 
1%." 

In  regard  to  the  second  patent  in  suit,  No.  962,678,  of  June  28, 
1910,  to  Sulman,  Greenway,  and  Higgins,  the  Court  quotes  part  of  the 
description  in  the  patent : 

"According  to  this  invention  the  crushed  ore  is  mixed  with  water 
containing  in  solution  a  small  percentage  of  a  mineral-frothing  agent 
(that  is  of  one  or  more  organic  substances  which  enable  metallic  sul- 
phides to  float  under  conditions  hereinafter  specified)  and  containing 
also  a  small  percentage  of  a  suitable  acid  such  as  sulphuric  acid,  and 
the  mixture  is  thoroughly  agitated ;  a  gas  is  liberated  in,  generated  in, 
or  effectively  introduced  into  the  mixture  and  the  ore  particles  come  in 
contact  with  the  gas  and  the  result  is  that  metallic  sulphide  particles 
float  to  the  surface  in  the  form  of  a  froth  or  scum,  and  can  thereafter 
be  separated  by  any  well-known  means.  Among  the  organic  substances 
which  in  solution  we  have  found  suitable  for  use  as  mineral-frothing 
agents  with  certain  ores  are  amyl  acetate  and  other  esters ;  phenol  and 
its  homologues ;  benzoic,  valerianic,  and  lactic  acids ;  acetones  and  other 
ketones  such  as  camphor.  In  some  cases  a  mixture  of  two  such  mineral- 
frothing  agents  gives  a  better  result  than  a  single  agent.  *  *  *  The 
present  process  differs  from  the  two  before  mentioned  types  and  from 
other  known  concentration  processes  by  the  introduction  into  the  acidi- 


404  FLOTATION 

fied  ore  pulp  of  a  small  quantity  of  a  mineral-frothing  agent,  that  is,  an 
organic  compound  in  solution  of  the  kind  above  referred  to  and  by  the 
fact  that  the  metalliferous  particles  are  brought  to  the  surface  in  the 
form  of  a  froth  or  scum  not  by  mechanical  means  but  by  the  attach- 
ment of  air  or  other  gas  bubbles  thereto.  In  the  frothing  process 
hitherto  known  the  substance  used  to  secure  the  formation  of  a  min- 
eral-bearing froth  has  been  oil  or  an  oily  liquid  immiscible  with  water. 
According  to  this  invention  the  mineral-frothing  agent  consists  of  an 
organic  compound  contained  in  solution  in  the  acidified  water. 'r 

The  Court  then  proceeds  to  say : 

' '  It  will  be  observed  that  no  one  of  the  claims  of  the  second  patent 
in  suit  requires  as  an  element  an  oily  substance  or  liquid  as  is  essential 
in  the  process  of  the  first  patent  in  suit,  and  all  of  the  claims  relied  on 
require  the  introduction  into  the  mixture  of  a  'small  quantity7  of  a 
'mineral  frothing  agent'  or  an  'organic  mineral  frothing  agent.'  The 
amount  of  the  mineral  frothing  agent  employed  in  the  process  is  not 
confined  to  a  fraction  of  one  per  cent  on  the  ore,  but  must  be  a  small 
quantity  evidently  to  be  determined  by  the  metallurgical  engineer  con- 
ducting or  superintending  the  operation  according  to  the  requirements 
of  the  different  ores.  The  novelty  of  this  invention  is  to  be  found,  not 
in  any  restriction  of  the  amount  of  the  mineral  frothing  agent  to  any 
stated  proportion,  for  there  is  none,  but  in  the  fact  that  a  mineral  froth- 
ing agent  as  the  means  of  separating  the  metallic  particles  from  the 
gangue  is  substituted  for  the  oil,  fatty  acid,  or  other  oily  substance  es- 
sential to  the  process  of  the  first  patent  in  suit.  Such  substitution  has 
produced  sucessful  results,  and,  I  think,  involved  invention.  Frothing 
agents  had  theretofore  been  used  in  ore  concentration,  but  not  in  the 
absence  of  an  oily  ingredient.  Even  were  the  grounds  on  which  the  va- 
lidity of  the  patent  can  be  sustained  less  clear,  it  should  have  the  bene- 
fit of  the  presumption  of  validity  arising  from  the  grant  of  letters. 
That  the  defendant  has  infringed  the  claims  in  suit  of  the  second  pat- 
ent is  established  by  the  evidence." 

The  third  patent,  No.  1,099,699,  was  not  sustained  and  need  not  be 
discussed. 

The  most  remarkable  feature  of  Judge  Bradford's  opinion  is  that 
he  states  flatly  that  the  Miami  is  using  the  process  of  patent  793,808 
yet  he  holds  that  the  company  has  infringed  patent  835,120,  the  num- 
bers of  these  patents  indicating  their  relative  age. 

An  analysis  of  the  decisions  up  to  date  shows  that  three  courts  out 
of  four  have  sustained  the  validity  of  patent  835,120  but  the  reasons 
have  been  dissimilar  and  even  contradictory.  For' the  sake  of  brevity, 


FLOTATION    LITIGATION  405 

I  shall  refer  to  the  courts  by  the  cities  in  which  the  issue  was  tried. 

Butte  said  that  Froment  did  not  anticipate  Sulman  et  al. 

San  Francisco  said  that  he,  and  others,  did  do  so.  This  court  re- 
fused to  consider  the  mere  diminution  in  the  proportion  of  oil  as  a  sub- 
ject for  patent. 

The  Examiner  of  Patents  had  decided  likewise. 

Washington  granted  validity  on  account  of  limitation  of  oil,  pecul- 
iar agitation,  and  peculiar  froth.  This  court  decided  that  Froment 's 
process  "was  little  more  than  a  laboratory  experiment"  and  did  not 
anticipate  the  workable  process  described  in  835,120. 

Wilmington  granted  validity  on  account  of  the  specification  of  crit- 
ical proportion  of  oil,  and  adversed  the  one  claim  that  did  not  specify 
that  limitation. 

Moreover,  the  Supreme  Court  differs  with  everyone  that  has  passed 
on  patent  835,120.  It  holds  the  Patent  Office  wrong  for  having  granted 
indefinite  claims,  it  holds  the  Butte  court  wrong  in  deciding  that  such 
indefinite  claims  were  valid,  it  holds  the  San  Francisco  court  wrong  for 
invalidating  the  whole  patent,  by  inference  it  holds  the  Wilmington 
court  wrong  for  basing  patentability  on  a  small  proportion  of  oil  alone. 

It  is  a  curious  fact  that  the  practicability  of  producing  an  effective 
froth  by  means  of  more  than  1  %  of  oil  was  not  tried  on  a  working  scale 
before  these  suits  were  started.  Such  experimental  demonstrations  as 
were  made,  out  of  court  or  before  the  judges,  were  apparently  uncon- 
vincing, for  the  sufficient  reason,  I  believe,  that  the  minimum  propor- 
tion was  considered  best  even  by  the  defendants,  but  as  soon  as  the 
Supreme  Court  had  given  its  opinion  and  placed  so  much  emphasis  on 
the  *  critical'  proportion,  the  use  of  more  than  1%  of  oil  was  applied 
successfully  on  a  scale  of  over  1000  tons  per  day  in  the  mills  of  the 
Utah  Copper  and  Butte  &  Superior  companies,  in  Utah  and  Montana, 
respectively.  The  *  critical'  point  was  proved  fallacious  early  in  1917. 

An  appeal  from  the  Wilmington  decision  was  taken  promptly  by 
the  Miami  company  to  the  Court  of  Appeals  for  the  Third  Circuit,  at 
Philadelphia,  where  the  case  was  heard  in  February  1917.  As  was  to 
have  been  anticipated,  the  appellees  made  the  most  of  the  Supreme 
Court's  decision  in  the  Hyde  case,  in  so  far  as  it  denned  and  limited 
the  scope  of  patent  835,120.  Counsel  argued  that  the  Miami  company 
had  not  infringed  because  its  operations  differed  radically  from  those 
described  in  the  Supreme  Court 's  decision,  both  in  the  kind  of  aeration 
employed  and  in  the  character  of  the  froth  produced.  Whereas  Hyde, 
and  Minerals  Separation  also,  used  mechanical  means  for  causing 
violent  agitation  and  for  producing  the  'cauliflower'  froth,  as  de- 


406  FLOTATION 

scribed  by  Mr.  Ballot,  the  Miami  company  used  a  Callow  cell,  an  in- 
clined trough  having  a  porous  bottom  through  which  compressed  air  at 
a  low  pressure  was  admitted,  producing  a  froth  without  the  aid  of  me- 
chanical agitation,  and  the  froth  thus  formed  was  described  as  thin, 
tender,  and  evanescent.  This  froth  broke  and  disappeared  as  soon  as 
the  supply  of  air  was  withdrawn,  while  the  froth  produced  by  beating 
air  into  the  pulp  would  last  for  days.  While  the  Miami  used  less  than 
1%  of  oil,  it  did  not  employ  the  two  other  elements  essential  to  patent 
835,120,  namely  the  violent  mechanical  agitation  and  the  formation  of 
a  peculiarly  coherent  and  persistent  froth.  It  was  argued  that  a  patent 
claim  for  a  combination  of  any  three  elements,  such  as  those  specified 
by  the  Supreme  Court  in  patent  835,120,  created  a  monopoly  only  in 
the  use  of  a  process  in  which  all  three  of  the  stated  elements  were  used. 
No  monopoly  was  secured  of  any  one  of  the  elements  used  singly  and 
apart  from  the  others.  Therefore,  there  was  nothing  in  the  Supreme 
Court's  decision  giving  Minerals  Separation  a  monopoly  of  the  use  of 
a  fraction  of  oil  per  se;  on  the  contrary,  the  Supreme  Court  stated  that 
the  patent  derived  its  validity  from  the  three  factors  taken  together. 
So  the  Miami  company  contended  that  it  had  a  perfect  right  to  use  any 
quantity  of  oil  however  minute,  provided  it  used  the  oil  in  a  process 
that  did  not  include  the  violent  agitation  and  the  persistent  froth 
characteristic  of  the  Minerals  Separation  process.'  Whereupon  the 
patentees  had  to  repudiate  the  limitations  specified  by  the  Supreme 
Court  and  depart  from  the  contention  that  they  had  made  in  the 
Hyde  case  concerning  the  special  and  remarkable  character  of  the 
froth  produced  by  their  process.  In  the  District  Court  the  great 
difference  between  the  two  kinds  of  froth,  one  due  to  beating  air  into 
the  pulp  during  violent  mixing  and  the  other  to  the  simple  introduc- 
tion of  compressed  air  through  a  porous  bottom,  had  been  emphasized 
heavily  and  the  statement  had  been  repeated  that  a  shovel  had  been 
seen  to  rest  on  the  froth  of  patent  835,120,  whereas  even  a  match  would 
sink  through  the  kind  of  froth  made  at  Miami.  In  the  appeal  at  Phil- 
adelphia another  tack  had  to  be  taken,  so  counsel  for  Minerals  Separa- 
tion, in  their  reply  brief,  stated : 

"With  respect  to  the  character  of  the  froth,  there  can  be  no  serious 
contention.  Before  the  discovery  of  these  patentees  nothing  in  the  na- 
ture of  froth  (a  collection  of  bubbles  on  the  surface)  remained  long 
enough  to  permit  recovery  of  the  metal.  By  reason  of  the  discovery 
of  these  patentees  a  froth  was  produced,  composed  of  'modified'  air 
bubbles,  coherent  and  persistent  enough  to  permit  of  recovery  of  the 
metal.  That  was  the  unique  thing — the  peculiarity  adverted  to  by  the 


.FLOTATION    LITIGATION  407 

Supreme  Court.  In  defendant's  practice  the  froth  produced  by  it  is 
similarly  composed  of  'modified'  air  bubbles,  and  so  is  coherent  and 
persistent  enough  to  permit  of  recovery  of  the  metal.  There  is  no  point 
and  nothing  of  importance  in  the  degree  of  coherency  or  persistency 
beyond  and  in  excess  of  that  required  for  the  recovery  of  the  valuable 
metal." 

The  decision  of  the  Court  of  Appeals  at  Philadelphia  is  expected 
at  any  moment.  Meanwhile  it  is  to  be  noted  that  after  Minerals 
Separation  won  the  preliminary  decision  in  the  Hyde  case  at  Butte 
they  brought  suit  against  the  Butte  &  Superior  company  and  moved 
for  a  preliminary  injunction.  This  was  in  the  autumn  of  1913.  The 
Butte  &  Superior  case  was  brought  before  the  same  court  as  that  in 
which  the  Hyde  case  was  first  tried,  and  this  court,  at  Butte,  ruled 
that  no  injunction  would  be  issued  if  the  Butte  &  Superior  company 
would  file  a  bond  and  also  file  monthly  reports  of  its  flotation  opera- 
tions with  the  Clerk  of  the  Court.  This  condition  was  fulfilled.  No 
injunction  was  issued  and  the  case  has  rested  in  statu  quo  up  to  the 
present.  The  trial  began  on  April  16,  1917.  It  proved  most  inter- 
esting because^  number  of  new  scientific  witnesses  were  placed  on  the 
stand  and  in  the  course  of  their  evidence  they  gave  the  results  of  recent 
research  into  the  principles  of  flotation.  In  my  article  on  this  phase  of 
the  subject  I  have  quoted  from  the  testimony  given  by  some  of  these 
gentlemen  at  Butte.  As  regards  the  legal  argument,  it  is  noteworthy 
that  the  'critical  point'  was  demolished  by  the  evidence  of  large-scale 
mill-operations  in  Arizona,  Utah,  and  Montana,  showing  that  the  use 
of  20  to  22  pounds  of  oil,  or  over  1%,  per  ton  of  ore  had  given  even  a 
higher  recovery  than  the  2  to  5  pounds  heretofore  customary  in  these 
mills.*  The  question  was  also  raised,  and  answered,  whether  the  ex- 
cess of  oil  was  inert.  Minerals  Separation  shifted  its  ground  so  as  to 
broaden  its  claims  to  cover  all  processes  in  which  an  air-froth  is  a 
factor,  regardless  of  the  amount  of  oil  used.  They  repudiated  the 
peculiar  agitation,  the  extraordinary  froth,  and  the  critical  proportion 
of  oil  on  which  they  had  obtained  a  favorable  decision  from  the 
Supreme  Court. 

[Since  the  above  was  written  the  Court  at  Philadelphia  has  re- 
corded its  decision  in  the  case  of  Minerals  Separation  v.  Miami  Cop- 
per Co.  This  decision,  made  known  on  May  24,  1917,  was  not  unani- 
mous, one  judge  (out  of  three)  dissenting.  The  majority  opinion 
upheld  the  validity  of  patent  835,120,  but  interpreted  the  Supreme 
Court's  decision  in  the  Hyde  case  as  meaning  that  "invention  resides 


* 'Flotation— the  Butte  &  Superior  Case.'    M.  &  S.  P.,  July  28,  1917. 


408  FLOTATION 

not  alone  in  the  critical  proportion  of  oil,  but  also  in  air  and  agita- 
tion." The  Miami  company  was  held  to  have  infringed  because  it 
used  agitation  similar  in  "degree  of  intensity  and  time  of  duration" 
to  that  denned  by  the  Supreme  Court  as  characteristic  of  the  pat- 
ented process.  Such  infringement  was  due  to  the  use  of  a  centrifugal 
pump  and  a  Pachuca  tank  before  aerating  the  pulp  in  a  Callow  cell. 
Inferentially  the  opinion  suggests  that  infringement  would  not  have 
been  found  if  the  Callow  cell  had  been  used  without  the  pump  and 
the  Pachuca,  both  of  which  were  discarded  by  the  Miami  company 
before  the  trial  began,  but  evidence  to  that  effect  was  not  in  the 
record.  Apparently  the  use  of  the  pneumatic  machine  in  flotation  is 
validated.  The  Court  says,  concerning  the  Callow  cell,  "Aeration  is 
direct  and  is  not  the  result  of  or  caused  by  agitation.  On  the  con- 
trary, agitation  results  from  aeration,  and  such  agitation,  though 
present  in  some  measure,  is  not  even  approximately  of  the  violence 
and  duration  of  the  agitation  of  the  patent. ' '  As  it  stands,  the  Phila- 
delphia decision  clears  the  ground  in  that  it  leaves  free  the  use  of  the 
Callow  cell,  and  other  pneumatic  machines  of  the  same  type,  in  con- 
junction with  such  agitation  as  was  used  in  the  priqj-  art  solely  for 
the  purpose  of  bringing  the  oil  in  contact  with  the  mineral  in  the 
pulp ;  in  other  words,  unless  the  use  of  flotation  involves  an  agitation 
characterized  by  great  intensity  and  long  persistence  it  will  not  in- 
fringe patent  835,120.  The  minority  opinion  confirms  this  view,  stat- 
ing that  "steps  of  the  process  'agitating  the  mixture  until  the  oil- 
coated  mineral  matter  forms  into  a  froth'  meant  the  novel  air-en- 
training agitation  which  the  patentees  disclosed,  and  did  not  cover 
the^novel  air-releasing  agitation  which  the  defendants  disclosed." 
The  majority  opinion  sustained  the  validity  of  patent  962,678  for  a 
"soluble  frothing  agent,"  but  tied  it  to  a  violent  and  persistent  type 
of  agitation.  On  the  other  hand,  the  exception  made  in  favor  of  the 
Callow  cell  as  not  infringing  835,120,  under  given  conditions,  was  not, 
apparently,  made  to  apply  to  metallurgical  operations  under  962,678 ; 
so  that  the  definition  of  what  is  a  'soluble  frothing  agent'  becomes 
crucial.] 

Some  reference  to  the  previous  litigation  in  England  and  Australia 
may  be  made,  although  it  is  now  only  of  secondary  importance.  It  is 
vital  to  the  proper  understanding  of  the  patent  litigation  as  a  whole 
to  recognize  the  fact  that  the  decisions  in  the  British  and  Australian 
cases  did  not  establish  the  validity  of  the  British  equivalent  of  II.  S. 
patent  835,120.  That  issue  was  not  before  those  courts;  indeed,  the 


FLOTATION    LITIGATION  409 

prior  art,  except  as  it  had  a  bearing  on  the  validity  of  the  Elmore  bulk- 
oil  patents,  was  not  under  consideration.  Moreover  it  was  the  Elmore 
bulk-oil 'patent  of  1898  and  not  the  vacuum-air  patent  of  1904  that  was 
at  stake.  The  question  before  the  British  and  Australian  courts  was  the 
validity  of  Frank  Elmore 's  British  patent  No.  21,948  of  1898  and  Stan- 
ley Elmore 's  British  patent  No.  6519  of  1901,  the  first  the  principal 
bulk-oil  patent  and  the  second  a  modification  specifying  the  use  of  acid. 
No  account  was  taken  of  the  patents  issued  between  the  dates  of  these 
Elmore  patents  and  the  date  of  the  Minerals  Separation  patent  of  1905, 
nor  was  the  question  of  how  such  intervening  patents  would  affect  the 
validity  of  835,120  considered.  To  establish  the  fact  that  Elmore 's 
bulk-oil  patent  is  not  valid  or  that  the  M.  S.  process  is  not  the  Elmore 
process  does  not  prove  anything  with  regard  to  the  validity  of  the  M. 
S.  patent.  That  question  was  not  before  the  British  courts  and  it  is 
remarkable  therefore  that  these  cases  should  have  been  cited  at  all  in 
the  American  courts.  The  effect  of  the  citation  has  been  only  con- 
fusing. 

Most  of  the  English  suits  were  between  Minerals  Separation  and  the 
Elmores,  or  the  company  with  which  they  were  identified.  Personal 
quarrels  and  charges  of  bad  faith  were  made  in  Sulman  &  Pi  card  v. 
Wolf,  in  1905,  and  in  Ore  Concentration  Company  [Elmores]  v.  Web- 
ster and  others  [the  Minerals  Separation  group]  in  1908,  but  the  two 
cases  involving  basic  patent-rights  were  both  brought  by  the  Elmores 
against  Minerals  Separation. 

In  the  first  case,  ended  in  1909,  British  Ore  Concentration  Syndi- 
cate, Ltd.,  and  Alexander  Stanley  Elmore  v.  Minerals  Separation,  Ltd., 
the  principal  issue  was  the  validity  of  the  Elmore  bulk-oil  patents  of 
1898  and  1901  against  the  Minerals  Separation  process  as  described  in 
British  patent  No.  7803,  the  equivalent  of  U.  S.  835,120.  The  Court 
(Mr.  Justice  Neville)  gave  judgment  against  the  Elmores  and  decided 
that: 

(1)  The  selective  action  of  oil  for  sulphides  was  known  before  El- 
more obtained  his  patents,  and  was  disclosed  in  prior  expired  patents. 

(2)  Elmore 's  patent  was  for  a  process  wherein  a  large  quantity  of 
oil  was  used,  sufficient  to  carry  all  the  sulphides  to  the  surface  by  the 
buoyancy  of  the  oil. 

(3)  The  Minerals  Separation  process  used  only  an  infinitesimal 
amount  of  oil  for  the  purpose  of  attaching  air-bubbles  to  the  sulphides, 
causing  them  to  float  by  the  buoyancy  of  the  air-bubbles,  and  did  not 
infringe  F.  E.  Elmore 's  patent. 

(4)  The  use  of  acid  in  oil  processes  was  known  before  A.  S.  Elmore 


410  FLOTATION 

obtained  his  patents  and  was  disclosed  in  prior  expired  patents,  there- 
fore, Elmore 's  patent  was  not  infringed  by  Minerals  Separation. 

The  plaintiff  appealed  and  the  decision  of  the  court  was  reversed,  it 
being  held  that  Minerals  Separation  was  infringing  the  1901  patent,  in- 
volving the  use  of  acid  with  oil.  The  Court  of  Appeals  found  that 

(1)  The  first  Elmore  patent  was  not  anticipated  by  previous  ex- 
pired patents  [such  as  those  of  Robson  and  Everson] . 

(2)  If  Minerals  Separation  used  a  thin  oil  they  would  not  infringe 
Elmore    [who  used  a  thick  oil;  so  also  Minerals  Separation  used  a 
thicker  oil  (oleic  acid)  than.is  now  customary  in  the  United  States]. 

(3)  The  second  Elmore  patent   [that  of  A.  S.  Elmore  of  1901] 
was  not  anticipated  by  previous  expired  patents  [such  as  Everson 's,  in 
which  acidulation  is  mentioned] . 

(4)  Minerals  Separation  infringed  the  second  patent  by  using  acid. 
An  appeal  was  then  taken  to  the  House  of  Lords  and  on  November 

16,  1909,  the  judgment  of  the  Court  of  Appeals  was  reversed,  that  of 
the  trial  court  being  upheld. 

The  Lord  Chancellor  (the  Earl  of  Loreburn)  said  that  the  Frank 
Elmore  patent  of  1898  need  not  be  discussed,  because  it  had  no  place  in 
the  controversy,  "into  which  it  has  nevertheless  been  introduced  with 
no  other  result  than  to  confuse  the  issue."  He  held  that  the  Stanley 
Elmore  patent  of  1901  was  "framed  with  great  subtlety,  b'eing  partly 
narrative,  partly  claim"  and  "designed  in  order  that  the  claim  might 
be  expanded  or  contracted  as  occasion  might  require  in  the  interest  of 
the  patentee ; ' '  that  the  only  definite  claim  was  for  acidulation.  and 
that  this  claim  was  anticipated  by  Everson ;  therefore  the  patent  could 
not  be  sustained. 

The  Earl  of  Halsbury  was  of  the  opinion  that  the  inventions  of 
Elmore  and  Minerals  Separation  were  "essentially  different,"  the  one 
being  dependent  on  ' '  the  selective  action  of  oil,  the  other  upon  surface 
tension ' ' ;  that  acidulation  had  been  '  *  invented  and  patented ' '  before 
the  date  of  Stanley  Elmore's  patent,  and  that  this  patent  was  so 
ambiguously  stated  that  it  should  be  held  bad. 

Lord  Atkinson  likewise  described  the  specification  of  the  patent  as 
"framed,  somewhat  craftily,  in  terms  of  studied  vagueness  and  am- 
biguity " ;  he  held  that  it  could  not  claim  ' '  the  mere  addition  of  acid  in 
small  quantities  to  a  mixture  of  ore,  water,  and  a  relatively  infini- 
tesimal quantity  of  oil  reduced  to  a  'freely  flowing  pulp'."  If  the 
patent  was  for  the  addition  of  a  small  quantity  of  acid  and  a  relatively 
large  quantity  of  oil  to  a  mixture  of  ore  and  water,  where  the  oil,  in 
accordance  with  some  obscure  law  of  affinity,  seized  upon  the  minute 


FLOTATION    LITIGATION  411 

particles  of  ore  in  preference  to  the  earthy  particles,  and/by  the  buoy- 
ancy of  oil,  floated  them  to  the  surface,  then  the  Minerals  Separation 
did  not  infringe  this  process,  because  their  process  was  one  where  they 
made  use  of  the  known  selective  action  of  oil,  yet  the  oil  was  used  :iii 
relatively  small  quantities,  and  the  metallic  particles  were  only  coated 
with  a  thin  film  of  it,  and  the  lifting  force  was  found,  not  in  the  buoy- 
ancy of  the  oil,  but  in  the  natural  buoyancy  of  the  air-bubbles,  which, 
introduced  into  the  mass  by  violent  agitation,  envelop  or  become  at- 
tached to  the  oiled  mineral  particles  and  raise  them  to  the  surface.  ; 

Lord  Shaw  of  Dunfermliiie  said:  "It  has  already  been  determined 
that  the  use  of  thin  oil  instead  of  thick  imports  no  infringement  of  the 
1898  patent,  nor  do  I  see  my  way  to  hold  that  there  has  been  any 
contravention  of  the  1901  patent  by  the  application  of  the  acid  to  a 
mixture  in  which  the  oil  has  been  reduced  from  bulk  to  the  merest 
fraction,  and  especially  when  froth  instead  of  oil  has  been  secured, 
along  with  the  law  of  capillarity  or  surface-tension,  as  the  main  float- 
ing and  separating  agent."  He  held  that  the  processes  were  es- 
sentially different  and  that  there  was  no  infringement. 

Lord  Ashbourne  concurred  with  the  decision  of  their  lordships, 
thus  making  the  judgment  of  the  Court  unanimous. 

Meanwhile,  in  1910,  the  Elmores  had  brought  suit  against  the  Sul- 
phide Corporation,  a  licensee  of  Minerals  Separation,  operating  at 
Broken  Hill.  The  issue  was  tried  in  Australia  with  a  result  adverse 
to  the  Elmores,  who  then  appealed  to  the  Judicial  Committee  of  the 
Privy  Council,  which  heard  the  case  in  November  1918  and  gave  a 
decision  on  March  6,  1914.  This  decision  confirmed  the  lower  court 
and  was  in  accord  with  that  of  the  House  of  Lords;  the  Judicial  Com- 
mittee found  that  the  Everson  patent  did  not  anticipate  the  Etmore 
acid-oil  patent,  but,  on  the  other  hand,  that  the  Minerals  Separation 
process  was  not  an  infringement  of  the  Elmore  patent,  because  it  relied 
on  surface-tension,  and  not  oil,  for  the  flotation  effect. 

I  quote  one  of  the  decisive  paragraphs  in  this  decision  of  the  Privy 
Council : 

' '  The  Appellants  place  considerable  importance  on  the  second  form 
of  apparatus  described  in  the  patent,  In  this  apparatus  a  thin  stream 
of  oil  is  thoroughly  mixed  with  the  pulp,  and  the  oil  'by  its  selective 
action  coats  or  absorbs  the  metallic  particles,  sulphides,  tellurides,  and 
the  like.'  The  whole  mixture  then  flows  over  a  weir  and  down  an  in- 
cline over  a  number  of  wave-like  steps  or  baffles  by  which  the  stream 
of  pulp  and  oil  globules  is  thrown  against  an  oiled  apron  continu- 
ously moving  in  the  opposite  direction.  Separation  is  effected  by  the 


412  FLOTATION 

oiled  surface  of  the  apron  taking  up  most  of  the  oil  globules  and  by 
also  picking  up  from  the  pulp  such  particles  of  metallic  substances  as 
have  escaped  oil  selection  in  the  mixer.  The  patentee  distinctly  draws 
attention  to  the  fact  that  separation  in  this  apparatus  does  not 
depend  upon  the  buoyancy  of  the  oil,  and  that  consequently  tar,  heavy 
residuum  oils,  and  other  like  substances  of  a  greater  gravity  than 
water  may  be  employed  as  the  selective  agent.  The  question  arises 
whether  the  selective  action  of  the  oil  or  tar  when  the  separation  is 
effected  by  the  second  apparatus  differs  from  the  selective  action  of 
oil  when  the  separation  is  effected  in  the  first  apparatus.  The  answer 
is  in  the  negative.  The  ' coating  or  absorbing'  described  in  connection 
with  the  second  apparatus  is  not  different  in  character  from  the  en- 
trapping described  in  the  first  apparatus.  The  'oil  globules'  hold  and 
carry  the  metallic  particles  and  are  taken  up  by  the  oiled  surface  of 
the  apron,  which  also  picks  up  from  the  pulp  such  particles  of  metal- 
lic substances  as  have  escaped  selection  by  the  oil. in  the  mixer,  that  is 
to  say,  such  particles  as  have  not  been  coated  and  carried  in  the  'oil 
globules'." 

Throughout  these  British  and  Australian  litigations  the  validity 
of  the  bulk-oil  patents,  of  1898  and  1901,  and  not  of  the  vacuum 
patent,  of  1904,  was  at  stake.  It  is  a  curious  fact  that  whereas  the 
Elmore  vacuum  method  depends  upon  surface-tension  and  the  use 
of  air  quite  as  much  as  the  Minerals  Separation  method,  it  was  not 
cited  in  the  litigation  and  it  was  ignored  by  the  courts.  It  is  also 
curious  that  during  the  six  years  of  litigation  in  the  United  States  the 
Elmore  vacuum  patent  was  not  used  to  attack  the  validity  of  835,120, 
although  this  patent  of  Minerals  Separation  was  taken  out  in  England 
on  April  12,  1905,  as  compared  with  Elmore 's  vacuum  patent  of 
August  16,  1904.  It  may  be  asked,  why  did  not  the  Miami  company 
fall  back  on  this  defence  and  use  Elmore  to  fight  the  Minerals  Separa- 
tion? The  answer  is  the  fear  to  establish  another  patent  monopoly, 
possibly  no  more  pleasant  than  the  one  already  on  the  ground.  How- 
ever, in  May  1915,  after  the  Miami  suit  had  been  heard  at  Wilmington, 
the  Elmore  vacuum  patents  were  purchased  for  $50,000  by  a  syndicate 
headed  by  Messrs.  D.  C.  Jackling  arid  J.  Parke  Channing,  represent- 
ing the  Utah,  Miami,  and  other  important  copper-mining  companies 
in  the  United  States.  It  is  possible  that  the  possession  of  these 
Elmore  patents  may  prove  an  interesting  factor  in  later  litigation,  but 
it  is  even  more  likely  that  the  use  of  oil  will  be  discarded  before  this 
litigation  is  ended. 


INDEX 


Page 

Absorption     158 

Acid,  effect  of   142,  221 

Adherence   of   bubbles   to   min- 
eral       190 

Adhesion    7 

Of  air  to  mineral 73 

Adsorption     156 

Selective    57,  135 

Agitation     7,  100 

Agitators  in  Magma  mill 249 

Air  and  gas 163 

Agitation  methods    25 

In  flotation 14,  141 

Alkali,  effect  of 221 

Effect  of  deflocculating 318 

Alcohol,   increasing   viscosity..     60 
Alkaline    chlorides 108 

Solutions    Ill 

Sulphides   Ill 

Anaconda  Copper  M.  Co 258,  264 

Treatment  of  slime 253,  264 

Anderson,  Robert  J...143,  145,  154 

Argo  mill    :..326,  391 

Atwater,    M.    W 244 

Avery,   Paul   W 395 

Bacon,   R.  F 362 

Beach,    F.    E 62 

Bains,  Thos.   M 200 

Bancroft,  Wilder  D..62,  70,  72, 

123,  134,  158,  197 

Beauchamp,  F.   A 18 

Braden  Copper  Co 254,  259 

Bradford,   Leslie    108 

Britannia  mill    246 

Bronze  powder  136 

Powder   experiment    62 

Bubble-films,    instability 152 

Stability   60 

Bubbles 7,  50,  54,  73,  162 

Adherence  to  mineral 190 

Coalescence  of   207 

Formation  of   50 

Function    of 217 

Bunker  Hill  &  Sullivan  mill.  . .   251 
Butte   &  Superior 407 

Calcium  sulphide  as  reagent...   373 
Callow,  J.  M.  .  .31,  161,  210,  234, 

287,  378,  402 


Page 

Callow   test-machine   93 

Canby,  R.  C 30 

Capillarity    40,  177 

Cattermole,   A.    R 19 

Case  machine  83 

Chalcocite,  effect  of  oil 68 

Chapman,  G.   A 22,  29,  133 

Chino   mill    376 

Choice   of   oil 125 

Classification   of   particles 308 

Coalescence  of  bubbles 207 

Coal-tar  creosote   13S 

Cobalt  ore   380 

Coghill,  Will  H 152,  172,  193 

Cohesion   of  water 173 

Cole,   David    31,  294 

Collectors    122,  143 

Colloid-slimes    347 

Colloidal  ores  307 

Sulphur    73 

Colloids 7,  159,   226,   305,136 

Books  on   325 

Classification  of  311 

Concentrate,  treatment  of 388 

Settling  in  bins  243 

Silica    in    255 

Smelting  of   256,  263 

Thickening  of 263 

Condition   of   oil 122 

Consumption  of  oil  126 

Contact-angle.. 47,  150,  178,  181,  204 

Contaminant   7 

Effect  of   41,     55 

Corliss,   H.   P 74 

Cost  of  flotation 192,  237,  335 

Critical  point 72 

Crowder,  Samuel  12 

Crown  King  mill  120 

Detroit  Copper  Co.'s  mill.  .251,  377 

Devereux,  W.  G 386 

Dewatering   concentrate 242 

Differential  flotation   102,  346 

Dispersoids 7,  311 

Dissolved  substances   104 

Durell,  C.  T 158,  206 

Dutch-App  mill    389 

Effect  of  air   141 

Of  dissolved  substances. .        .  167 


414 


INDEX 


Page 

Effect  of  quartz .. 195 

Of  temperature 166 

Electrostatic   phenomena    160 

Electrostatics     200,  331 

Elmore,  F.  E 13,  25,  409,  412 

Emulsions     7,  159 

Stability  of   169 

Emulsoids  and  suspensoids. . . .  312 

Engels  copper  mill 250 

Evaporation  of  film 162 

Everson,  Carrie   11 

Experiment,  bronze  powder. ...  62 

To  show  viscosity  of  film. ...  60 

With  alcohol . .  136 

With  mercury   . , 188,  191 

With  mineral   215 

With  quartz 191 

-With  quartz  and  galena 202 

Fields,  J.  D .   300 

Film-flotation     . . 76,  180 

Suspension    . 9 

Film  of  liquids  .  .180,  187 

Fine  grinding  of  ore. 73 

Floeculation     . ........  314,  316 

Flocculent    7 

Flotation  agents    74 

And  selective  adsorption....  144 

Armor  193 

At  Broken  Hill    15 

Cell     231,  235 

Chalcocite     68,  230 

Chalcopyrite    379 

Copper  carbonate    374 

Cost   of    192,  388 

Differential 102,  345 

Early  attempts 10 

Effect  of  air   141 

Lead  carbonate    365 

Lead  sulphate 102,  105,  393 

Of  gold 379,  382,  386,  389,  395 

Silver 380,  385 

Tellurides   380,  395 

Zinc  ore  . .  .102,  105,  110,  140,  378 
Flotation  machines: 

Callow 286,  288,  289 

Cole    &   Bergman 296,297 

Eberenz  and  Brown 265,  268 

Fagergren   &  Green 279 


Page 

Grondal    301 

Hebbard-Harvey     284 

Higgins     276 

Higgins  &  Stenning 274 

Hoover    82 

Hyde    290 

Inspiration    295 

Janney    271,   272,  273 

K.   &   K 269 

Launder    294 

Livingston     303 

Minerals  Separation   266 

Mischler  280 

Norris     299 

Ohrn    300 

Owen  275 

Rork    268 

Rowand    304 

Wood     277 

Flotation-oils,    properties    of...  131 

Products,  disposal  of 242 

v.  Cyanidation    385,  391,  394 

Flow-sheet : 

Argo   mill    392 

Calaveras  copper  mill 229 

Formation  of  bubbles 148 

Fractional   roasting    102 

Free,  E.  E 172,  305,  347,  358 

Froth 8,  162 

And  quartz 193 

Disposal  of    98 

Formation  of 223 

Persistence  of   123,  167 

Frothers     70,  121,  143 

Frothing  agents    143,  203 

In  cyanide  solution.... 395 

Gahl,  Rudolf.  .133,  192,  197,  227, 

292,  376 

Galena  on  water 156 

Garfield  Smelting  Co 258 

Gas  in  flotation 16,  19,  77 

Gold  ore,  flotation  of 379 

Grease 8 

Effect  of    35,  41 

Natural 74 

Greenway,   H.   H 105 

Grinding  of  ore 73,  95 

Hamilton,  E.  M .  395 


INDEX 


415 


Page 

Handy,  R.  S 287 

Haynes,  William    11 

Hebbard,  James  22 

Higgins,  A.  H 22,  132 

Hildebrand,  Joel  H 165,  192 

Hoover,  T.  J 17,  18,  27,  31, 

45,  75,  148,  205 

Horwood  process    102,  239 

Hoveland,    H.    B 362 

Hyde,   J.   M. 27,  29,  351 

Suit    397 

Hydrogen  sulphide  as  reagent.  366 
Hypothesis  explaining  flotation  72 
Hysteresis  149,  205 

Inspiration  mill    254,  292 

Instability  of  bubble-films 152 

Interfacial    tensions    214,219 

International  smelter  .  .   259 


Janney,   F.   G. 
Janney,   T.   A 


80 
29 


Kenrick,    Frank   B 44 

Kirby,  E.  B....: 26 

Labor  in  flotation   192 

Laist,    F 264,  320 

Lead  carbonate,  treatment  of..  365 

Lewis,   Robert   S 242 

Lime  as  a  flocculating  agent..  320 

Litigation     397 

Lockwood    349,  351 

Loring,   W.   J... 389 

Lowering  of  surface-tension...  153 

Lyster,   F.   J 106 

Macquisten,   A.    P 26 

Manganese    compounds 112 

Manipulation    75,  94 

Mathewson,    E.    P 172 

Mexican  mill 384 

Measurements  of  tension 213 

Mechanical    development    265 

Melones  mill   386 

Metallic     8,  71 

Miami  Copper  Co 31,  247,  402 

Mill,  Whimwell    351 

Mineral  particles  and  air 69 

Minerals,  the  flotation  of..        .  154 


Page 

Minerals    Separation 19,    22, 

23,  402,  409 
Molecular  forces  in  flotation...   172 

Mount  Morgan  mill 261 

Mueller,   W.   A 125 

Murex   process 349 

Nevada  Consolidated    234 

Norris,  Dudley  H 146,  175,  396 

North  Star  mill    103,  381 

Nutter,    E.    H 27,  132,  387 

Oil   buoyancy    9 

Condition  of   122 

Consumption   of    71,  126 

Cost  of 192 

Choice  of  125 

Definition    7,  121 

Film    experiments    in    Miami 

law-suit    63,  67 

For  flotation    232,  334 

Mixture  of  224 

On  chalcocite    68 

Selective    action    163 

Testing  of   96 

Troubles  with    327 

Quantity  of 32,  71,  222,  393 

Varieties  of ... 129 

Over-oiling     . 124 

Oxidized  ores,   treatment  of...  360 

Patents : 

Bacon,  Raymond  F..103,  362,  364 

Bradford,   Leslie 108 

Dick,  F.  B 360 

Green  way,   H.   H 105 

Higgins,   A.    H 132 

Horwood,  E.  J 102 

Hoveland,  H.  B .362,  364 

Lavers,  Henry    104 

Lyster,  F.  J .....106,  111 

Minerals    Separation 

109,  111,  113,  116 

Nutter,  E.   H ..114,  132 

Owen,   T.  M 112,  115 

Ramage,  A.  S 102 

Schwarz,  Alfred  361 

Sulman  &  Picard   .104,  361 

Terry,  J.  T 362 

Wentworth,  H.  A 102 

Pearce,   Jackson  A . .  .   391 


416 


INDEX 


Page 

Persistence  of  froth 123 

Pine-oil    126,  12^,  163 

Pneumatic  flotation    92 

Portland   mill    250,  294 

Potter,   C.   V 15 

Power  in  flotation  mill 192 

Process,  Cattermole    21 

De  Bavay 17 

Delprat 16 

Elmore    13 

Horwood     239 

Potter     15,  108 

Prince  Consolidated  mill 372 

Properties  of  flotation-oils 131 

Quartz,   effect   of 195 

Ralston,  O.  C 75,  102,  121, 

265,  320,  335,  345,  360 

Ramage,  A.  S 102 

Raw  oil,  effect 125 

Retarder     108 

Recovery  in   mill. 227,  231,  236,  393 

Resin-oil    126,  130 

Rickard,  T.  A.  .7,  9,  34,  246,  379,  397 

Roasting  concentrate   257 

Robbins,   Hallett  R 31,  228 

Roy  &  Titcomb  machine 87 

Royalties 341 

Saponine,    effect    of 63,209,213 

Saponification    8,  162 

Schwarz,  Alfred 361 

Schwerin,  B 347,  349 

Selective  action  of  oils 163 

Adsorption     57 

Separatory  funnel  90 

Silica  in  concentrate 255 

Silver  ore,  flotation  of 380 

Simpson,  W.  E 74 

Slide  machine    86,  88,  89 

Slime    in    flotation 345 

Smelting    of    concentrate 256 

Smith,  H.  Hardy 146 

Sodium  sulphide,  as  reagent...  368 

Cost  of   371 

Speed  of  agitation 100 

Stability   of   foams 167 

Sulman,    H.    L 11,20,  48 

Sulman  &  Picard 18,  19,  32, 

104,  361,  397 


Page 

Sulphatization    239 

Sulphidizing  of  copper  carbon- 
ate       374 

Lead   carbonate    365 

With  sodium  sulphide 369 

Zinc  ore    .  . . 37S 

Surface-tension     35,  148,  154 

Effect  of  temperature 166 

Lowering  of    153 

Measurement    43,  45,  165 

Of   water    174 

Suspensions,   stability   of 171 

Taggart,  A.  F 54,  60,  62,  68,  69 

Temperature,  effect  on  flotation  329 

Tenacity  of  bubble 151 

Terry,  J.  T. 362 

Testing  machines: 

Callow     93 

Case     83 

Glass  jar    91 

Janney    79 

Owen  92 

Potter-Delprat 78 

Roy  &  Titcomb. 87 

Separatory    funnel    90 

Slide    89 

Suan 85 

Wood 77 

Testing    of    oils 96 

Testing  ores  for  flotation 75 

Theory   of  flotation 34,   134, 

146,  165,  202,  211,  330 

Thickening  of  concentrate 263 

Thornberry,  M.  H 377 

Towne,  R.  S 31 

Treatment    of    slime    at    Ana- 
conda       264 

Van  Arsdale,  G.  D 122 

Varieties  of  oil 129 

Viscosity    8,     58 

Effect  of  alcohol 60 

Experiment 60 

Of  bubble  films 60 

Wetting    46,   134,   170,   184,  217 

Wood,  H.  E 16 

Wood  machine   77 

Wood-creosote  .   129 


Yerxa,  >R.   B 


62 


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